The New York Times, by Staff

By Leslie H. Gelb

President Reagan's vision of defensive systems to render nuclear weapons ''impotent and obsolete'' is moving strategic thinking and nuclear competition toward a new era.

For Mr. Reagan's vision has done nothing less than to assault the core of nuclear philosophy, namely deterrence based on the threat of retaliation. He and his senior aides are saying that the 40 years of nuclear peace built on that threat cannot last and is, in any event, immoral.

Most experts say they think that perhaps decades of research will be required before they know with confidence whether the vision can be translated into workable technology.

Yet proponents and critics alike are well aware that the vision itself, along with accelerated research programs and the attending debates, is shaking the foundations of American military policy - strategic doctrine, the shape of military spending, alliance relations and arms control.

National attention is focusing more and more sharply on the plan as the two superpowers prepare to resume arms talks in Geneva on March 12, as current research and testing proceeds apace, as Congressional debate gets under way on proposed spending for such research and more and more technical and doctrinal questions emerge.

The President's ideal is a defensive system that saves lives. But the reality could be new and more powerful offensive and defensive capacities that could be used for a decisive nuclear first strike. Thus, the debate centers on how far the reality is from the ideal: Is the President's so-called Strategic Defense Initiative, more popularly known as ''Star Wars,'' well conceived to save countless lives and enhance deterrence, or is it more likely to lead to an ever-more-precarious nuclear balance?

For the next five years, planned spending is about $30 billion out of more than a trillion dollars in military budgets. When and if the program gathers momentum thereafter, it could become a dominant element of that budget.

Publicly, American allies are supporting research. Privately, they continue to express the deepest fears that the program will bring a space arms race that will reduce or eliminate the links between American security and their own.

Administration officials assert that the Strategic Defense Initiative brought the Soviet Union back to arms talks and will lead to real reductions in offensive arms. But Soviet leaders insist they will make no such reductions until the program is reined in. And Mr. Reagan said in a recent interview that he would not limit his initiative, even if Moscow agreed to deep reductions in missiles and even if all nuclear forces were eliminated. Administration officials also say he has put aside his earlier offer to share defensive technologies with Moscow.

Publicly, the Administration says the Soviet Union already has the jump in missile defense, both in a deployed antiballistic missile system and in development of new technologies. Indeed, no one disputes that the Russians have a small ABM system around Moscow and that the United States has not deployed a system. Privately, however, the weight of opinion in the Administration is that hard American knowledge of Soviet research in this area is negligible and that the United States leads in most if not all areas of research.

All of the agonizing decisions and judgments that will have to be made in years to come on developing and deploying a panoply of the most futuristic technologies will have to be done without ever testing them against a full-scale attack. And to fulfill their goal, as former Defense Secretary Harold Brown has written, they will have to work perfectly ''the first time.''

The unanswered questions now seem legion. Has the momentum for the proposed program already made it unstoppable? What, in fact, is the Soviet technical ability? How was the idea of a vast American anti-ballistic missile system revived when it seemed so firmly put to rest by treaty more than a decade ago? Who is behind it? Who is against it? Why? Can it ultimately be made to work? Can these defensive abilities also be used as potent offensive weapons?

What is perhaps most striking about a series of recent interviews with officials throughout the Administration is that hard questions about the program are not getting much of a hearing in the inner councils. By almost all accounts, support for the program has become the touchstone of loyalty to the President.

In fact, whether some of these questions will be answered may depend on the purview of the debate. And that may depend on who defines its terms - the Administration or its critics in Congress and the arms control field.

Officials acknowledge that the Administration wants the vision to dominate what they see as a narrow and practical debate about research into promising technologies.

The critics want to cast the debate in the broadest possible terms now, before the program becomes enormous and politically unstoppable.

Officials and critics alike agree that some research is desirable, if only on the ground of prudence and as a check against Soviet projects.

Moreover, it should be pointed out that neither critics nor Soviet leaders who publicly argue for limits on military research have put forward a plan for monitoring work that for the most part occurs in laboratories.

Mr. Reagan opened the door to the larger debate when he unveiled his ideas on March 23, 1983. In calling on scientists to find ways to render nuclear weapons ''impotent and obsolete,'' he said, ''My fellow Americans, tonight we are launching an effort which holds the purpose of changing the course of human history.''

Mr. Reagan and his senior aides say by way of justification of the program that they want to escape the nuclear nightmare by going from deterrence based on offense or the threat of retaliation to deterrence resting on defense or the security of protection. On moral grounds, this is also consistent with positions on nuclear war recently taken by the Roman Catholic bishops of the United States.

It is precisely the problem that Mr. Reagan's predecessors from Lyndon B. Johnson on wrestled with. They all said ''No'' to making the transition from mutual assured destruction to mutual assured defense, in which attacking missiles would be destroyed before they could reach the targets. Their objections were based largely on the ground that such defensive systems were not feasible.

Now, Mr. Reagan and many of his advisers maintain, this has changed. ''Current technology,'' he said in unveiling his plan, ''has attained a level of sophistication where it is reasonable for us to begin this effort. It will take years, probably decades, of effort on many fronts.''

All the worse, charged a host of American scientists, arms control specialists and the Soviet Union. Rather than a more stable and sensible peace, they argued, Mr. Reagan's vision would touch off a new and more dangerous arms race in space and succeed only in destroying prospects for arms control. Soviet officials are saying privately that they will have to accelerate their research program and keep open the option of making more offensive nuclear warheads to overcome prospective defenses. They also express concern that once the research program gains momentum, future American Presidents will find it difficult to stop. They argue that a system to defend populations will not work, but they do tend to think it might be possible to build a limited system for the defense of missile sites. Still, they do not want to open this door either.

As for feasibility and rendering nuclear weapons obsolete, former Defense Secretary Brown, a nuclear physicist, spoke for scientists who are critics of the program when he wrote recently, ''The combinations of limitations - scientific, technological, systems engineering costs - and especially the potential countermeasures make the prospect of a perfect or near- perfect defense negligibly low.''

Lieut. Gen. James A. Abramson Jr., the director of the Strategic Defense Initiative, disputed this in an interview, saying: ''There is very little question that we can build a very highly effective defense against ballistic missiles someday. The question is how soon and how affordable and what degree of effectiveness can initial steps allow us.'' As for those who disagree, he suggested that it was ''because for a lifetime they have been dedicated to another idea and they are not very willing to accept a new thought process.''

''What is really happening,'' he said, ''is that there are a large number of dedicated, talented people working on this in Government and industry. And when they all have a goal to march to, and that's what the President gave us, you just cannot stop the progress they are making and that progress is what's happening.''

Officials say President Reagan's 1983 speech was inspired in part by his monthly meetings with the Joint Chiefs of Staff, who proposed rethinking the idea of developing defenses to protect missile sites.

Mr. Reagan, in effect, enlarged this notion, and his speech was viewed by Administration officials as essentially a way of telling them that this was one of his top priorities, perhaps his ultimate legacy. He made few concrete decisions about the program other than to approve an increase in spending of about 50 percent over six years, an increase from about $20 billion to about $30 billion.

His senior aides, many of whom acknowledged being taken by surprise, proceeded to fill in the blanks and push their own views, often in contradictory ways.

''It's all things to all people,'' commented Paul C. Warnke, a director of the Arms Control and Disarmament Agency under President Carter. ''To the President, it is saving people’s lives. To Defense Secretary Weinberger, it is a technological stepping-stone from missile defense to the President's larger conception of immaculate defense. To others, it is simply a means of defending missiles. To some, it is a bargaining chip in arms control negotiations, while to others, including the President, it is untouchable.''

As matters stand, the Administration is asking Congress to approve $3.7 billion this year, after $1.4 billion last year, for research on what is envisaged as a three-tier defensive system.

The first line of defense would be in the three- to five-minute boost phase as a missile with its warheads is rising to leave the atmosphere. The second would be in the midcourse flight in space of about 20 minutes when the warheads or reentry vehicles separate from the missile. The terminal phase is the last two minutes of flight as the warheads re-enter the atmosphere.

Broadly speaking, the technological innovations come for the most part in the first two phases. Here the Administration is looking at an array of possibilities: space- and ground-based lasers, magnetic rail guns that fire projectiles at amazing speeds and directed beams of subatomic particles.

As the skeptics see it, this automatic and automated situation would require almost immediate reaction and could effectively remove the possibility of human decision - even by the President. And in the past, of course, even the 25-minute flight time of intercontinental missiles was regarded as short and always a matter of concern.

The terminal phase of the defense would use existing and more conventional technologies of firing a missile at an incoming warhead. Advocates say this technology could be deployed within a decade.

The Administration remains divided on the feasibility and importance of the idea. At one end are the doctrinal purists such as Fred C. Ikle, Under Secretary of Defense for Policy, who said recently: ''The Strategic Defense Initiative is not an optional program, at the margin of the defense effort. It's central, at the very core of our long-term policy for reducing the risk of nuclear war.'' Like the technological optimists such as General Abramson, they believe not only that it can be done, but also that it must be done.

There are also those who would wait and see, such as Paul H. Nitze, the primary arms control adviser to Secretary of State George P. Shultz. In a recent speech, Mr. Nitze stated, ''Quite frankly, it may prove impossible to obtain.''

No longer is any official saying publicly what Richard D. DeLauer, former Under Secretary of Defense for Research and Engineering, said in 1983. ''This is a multiple of Apollo programs,'' in terms of the technological advances required, he said, and if it is deployed, Congress will be ''staggered at the cost.'' Still, some officials privately believe this to be the case.

The basic doctrine behind the Administration's position is that the United States cannot be sure mutual assured destruction will work into the next century and that it must be replaced by mutual assured defense.

The centerpiece of the nation's strategic thinking until now has been the Antiballistic Missile Treaty of 1972, and for now it continues to be. This limited the superpowers to no more than 100 defensive missiles, all defending one site. It was taken by Washington to mean that both sides accepted the doctrine of mutual deterrence through retaliation and that neither would do anything to take away the other's ability to retaliate devastatingly.

Thus, Article V states, ''Each party undertakes not to develop, test or deploy ABM systems or components which are sea-based, air-based, space- based or mobile land-based.'' This did not preclude research, which both sides have been doing since then, nor could it make absolute distinctions between research and development.

Acceptance of the treaty was also predicated on the assumption that reductions in offensive arms would follow swiftly and that otherwise Washington would reconsider its adherence to the treaty.

The Administration is saying that quantitative and qualitative improvements in offensive weapons, particularly in the powerful and accurate Russian land-based missiles, are threatening to neutralize the American retaliatory capacity.

Officials contend that a few hundred missiles with multiple warheads could destroy virtually all American land-based missiles, submarines in port and bombers on airfields. This would leave future Presidents with only submarine-launched ballistic missiles of insufficient accuracy to destroy anything but Soviet cities. This, they say, is not a credible retaliatory threat because an attack on Russian cities would necessitate an attack on American population centers.

Thus, their argument runs, Washington must build better offensive systems or defensive systems or both.

The Administration is proposing to do both. It is building offensive weapons such as the Trident II and cruise missiles, which would have the accuracy to strike hardened Russian targets such as missile silos and command centers, not just cities. Also for offense, it is developing a small missile known as Midgetman, which Moscow could not count on destroying because of its mobility.

The United States is pushing these programs even though the President's Commission on Strategic Forces said the so-called window of vulnerability that they were designed to overcome had been overestimated. And the Administration has not dismissed the ''nuclear winter'' theory that says the smoke and dust from even relatively few nuclear explosions would shut out enough sunlight to end human life on the planet.

Officials say the new offensive programs are not enough.

Whatever the reality of the strategic balance the new offensive weapons produce, officials say, the perception of Russian superiority will remain because of the powerful land-based missiles. This perception, they contend, would put Presidents in a weak position in future crises.

Asked why they cannot, through public statements, make the perceptions conform to the reality, the answers are generally vague. Instead, they argue that greater and greater offensive power will only make the nuclear balance more unstable. Thus, to them, defense against attacks on missiles - from small or accidental attacks to all- out attacks - is the only moral and practical answer.

Skeptics and critics raise two principal objections to this line of reasoning: It remains easier and cheaper to overcome defenses with offensives than to neutralize offensives with defenses; and in the critical and long transition period from relying on offense weapons to relying on defensive weapons to prevent war, the likelihood of nuclear war would be at its peak.

Mr. Reagan recently argued that the defense could prevail, as it did in World War I when gas masks were an effective defense against chemical warfare. Others suggest that the use of poison gas was stopped when an increase in its use threatened to destroy both sides without benefit to either.

The more typical answer from the Administration comes from Mr. Nitze, who said: ''New defensive systems must also be cost-effective at the margin, that is, it must be cheap enough to add additional defensive capability so that the other side has no incentive to add additional offensive capability to overcome the defense. If this criterion is not met, the defensive systems could encourage a proliferation of countermeasures and additional offensive weapons to overcome deployed defenses, instead of a redirection of effort from offense to defense.''

Also, as defenses against ballistic missiles are deployed, each side could increase its number of aircraft and cruise missiles flying in the atmosphere to circumvent them. To this, Administration officials reply: Better these slower-flying weapons, which allow time for response, than the fast- flying missiles.

As to the transition period, Mr. Ikle contends that it would not be destabilizing. He says, ''As a growing fraction of the Soviet missiles could no longer reach their targets, Soviet planners would face increasing uncertainties and difficulties in designing a rational first strike.''

Not so sanguine is Mr. Nitze, who said the transition could take decades, could be tricky and would be dangerous if Moscow developed better defenses first. ''We would have to avoid a mix of offensive and defensive systems that, in a crisis, would give one side or the other incentives to strike first.''

The real fear felt by critics is that the side that got to the optimal mix first might reason that it could destroy most of the other side's forces in a first strike and blunt the retaliatory blow with defenses. This, in theory, would make nuclear war ''rationally'' thinkable for the first time.

Mr. Reagan and others say the transition could be managed through arms control negotiations by agreeing on what to deploy and when. Officials say he no longer is willing to share the technology with Moscow because it could be put to many other military and civilian uses. Critics argue that such negotiations would be far more difficult than anything yet undertaken with Moscow.

While critics take the Administration's line to mean that a change in doctrine has already occurred, officials say otherwise. Richard N. Perle, Assistant Secretary of Defense for Policy, said in a recent interview: ''It is not true that we've already made the decision to abandon mutual assured deterrence or the policy that seeks to achieve security by the threat of retaliation. That will still be with us for years.''

Officials such as Mr. Perle and Mr. Nitze seem far less concerned with the President's ultimate vision than with what they see as the closer and realizable goal of defending American land- based missiles. They argue that this would enhance deterrence by substantially reducing the Soviet chances of destroying these fixed targets in a first strike.

Critics of this view of enhanced deterrence say a system to defend missiles could readily blossom into a defense of the general population, putting the debate virtually back where it started.

This fiscal year, research on missile defense constitutes about 5 percent of the Pentagon's research and development budget. By 1990, the Congressional Budget Office estimates, it will rise to 17 percent.

General Abramson questions these figures and feels even more strongly about estimates of deployment costs, which he says will not be known until the Government finds out which systems will work.

Nonetheless, estimates by many experts run from half a trillion to a trillion dollars. This does not include the cost of a possible air defense system, which former Defense Secretary James R. Schlesinger said could be as much as $50 billion over several years.

Even smaller guesses would be far more than is being spent on offensive nuclear programs and would consume the bulk of spending on strategic forces. Pentagon analysts also say that deployment would bite deeply into spending on conventional forces.

Some Pentagon analysts argue that missile defenses are good for Western Europe and Japan. These analysts say that in the short run, protecting the United States will lend credibility to Washington's threat to use nuclear weapons to protect them. In the long run, they hold out the promise of extending the protective umbrella to the allies as well.

But the allies did not see it this way at first, and Administration officials say that Mr. Reagan worked out a deal with Prime Minister Margaret Thatcher of Britain to patch over the disagreements. In effect, the agreement is that the allies - minus France - will publicly support research, and in return the Administration will consider decisions on the ABM treaty and deployment to be matters for allied consultations and negotiations with Moscow.

In the meantime, Britain and France are concerned that an American defensive system would make the Soviet Union develop a full-scale system that could negate French and British nuclear missiles. Their concern is that the Soviet network might not be good enough to block an American attack but might be good enough to neutralize the West European deterrent.

The allies in general are worried that in the short term, defensive systems to protect the superpowers will make Europe alone the likeliest nuclear battlefield.

Finally, West European diplomats worry that uncertainty about American plans for defenses will complicate and perhaps undermine the chances for progress on arms control and particularly on reducing medium-range nuclear forces in Europe.

Administration officials maintain that Mr. Reagan's defense initiative brought Moscow back to the bargaining table it left in late 1983 when the first American medium-range missiles were deployed in Europe. They also argue that the specter of competing with the United States in this area will drive Moscow toward concessions on reducing offensive forces.

The officials have said that when Soviet and American negotiating teams convene in Geneva on March 12, the Americans will try to persuade the Russians to accept a three-stage approach: radical reductions in offensive forces, then a transition to a mix of offensive and defensive weapons and finally the total elimination of nuclear weapons and deployment of full- fledged defenses.

As explained by the Administration, bargaining leverage would be derived from Moscow's fear of engaging in an all-out technology race with Washington. At the same time, the officials acknowledge that this leverage depends on how much Congress supports the strategic programs - the Strategic Defense Initiative and the MX missile in particular - and that Congressional support depends on the sense that the Administration is negotiating in good faith.

So far, Moscow has totally rejected the Administration's approach. The Soviet position is that Moscow will not commit itself to a radical reduction in offensive forces until it knows that defenses will be limited.

But Moscow has not spelled out exactly what limits it wants on defenses. Soviet diplomats here are well aware that laboratory research cannot be monitored effectively, and the feeling among American officials is that Moscow is simply conducting a propaganda campaign to try to reduce public support for the Administration's research program without curtailing its own research.

Administration officials voice special concern about a Soviet radar system nearing completion in the central part of that country. They contend that this is a clear violation of the ABM treaty, while Moscow answers that it is merely a satellite tracking station. Administration officials vow that this will be a key issue in the coming talks.

There matters stand on arms negotiations, with neither American nor Soviet officials evincing much optimism that they will be able to solve these problems through negotiations.

The prevailing view in the Administration is that whatever effects defensive prospects ultimately have on negotiations, the immediate effect has been to create a deadlock.

By William J. Broad

In January 1982, Dr. Edward Teller, a physicist who played a central role in developing the hydrogen bomb, met with President Reagan to discuss new ways of trying to destroy enemy missiles and warheads during an attack.

It was the first of four meetings Dr. Teller would have with the President before the ''Star Wars'' speech of March 23, 1983. In that address Mr. Reagan called on American scientists to find ways of rendering nuclear weapons ''impotent and obsolete.''

No one - perhaps not even Mr. Reagan - can definitively list all the factors that ultimately prompted him to make his speech. Dr. Teller's counsel over the course of a year may have played a role. But so did the suggestions of key confidants, his science adviser, the Joint Chiefs of Staff and the National Security Council. Indeed, a confluence of people and ideas, of forces and counterforces, lay behind the speech, and a review of that history goes a long way toward illuminating the origins of the Strategic Defense Initiative, as it is officially called, and clarifying the debate that swirls around it today. Central to the story is Ronald Reagan himself. Even before assuming the Presidency, he had expressed strong interest in trying to defend the nation from enemy missiles and had shown a curiosity about the powers of high technology. Newly elected to public office in 1967, Mr. Reagan became the first Governor of California to visit the Lawrence Livermore National Laboratory in Livermore, Calif., one of the country's premier facilities for research on weapons and such exotic technologies as laser fusion. It had been founded by Dr. Teller in the 1950's.

''We showed him all the complex projects,'' Dr. Teller recalled in an interview. ''He listened carefully and interrupted maybe a dozen times. Every one of his questions was to the point. He clearly comprehended the technology. And there was no skimping on time. He came in the morning and stayed over lunch.''

In 1980 during the Republican Presidential primary campaign, Mr. Reagan, recalled a tour he had recently taken of the North American Defense Command, a secret installation in a hollowed-out mountain in Colorado, and said he was perplexed at the lack of space-based defense.

''They actually are tracking several thousand objects in space, meaning satellites of ours and everyone else's, even down to the point that they are tracking a glove lost by an astronaut,'' he was quoted as saying in the book ''With Enough Shovels'' by Robert Scheer. ''I think the thing that struck me was the irony that here, with this great technology of ours, we can do all of this, yet we cannot stop any of the weapons that are coming at us. I don't think there's been a time in history when there wasn't a defense against some kind of thrust, even back in the old-fashioned days when we had coast artillery that would stop invading ships.''

Mr. Reagan's sentiments were in step with those of the Republican Party, which in its platform, adopted on July 15, 1980, called for ''vigorous research and development of an effective anti-ballistic-missile system, such as is already at hand in the Soviet Union, as well as more modern ABM technologies.'' It also called for new offensive missiles and an ''overall military and technological superiority over the Soviet Union.''

Soon after the election, President- elect Reagan questioned Senator Harrison H. Schmitt - a former astronaut and chairman of the Senate Subcommittee on Science, Technology and Space - about the feasibility of building a space-age defense.

''The meeting lasted about about 20 minutes,'' Mr. Schmitt recalled in an interview. ''We were talking about science and technology in general. Then, about halfway through the session, he made a statement that he was concerned that we could not just keep building nuclear missiles forever - that ultimately their proliferation would get us into serious trouble. He asked what I thought about the possibility of strategic defense, especially with lasers. We spent half the conversation talking about it.

''When I later heard his speech, the phrases sounded very familiar,'' he said. ''The words had the same ring.''

Way to End MAD Strategy

In the early days of his Administration, Mr. Reagan put his questions about space-based defense to a number of scientists and experts. Not the least enthusiastic was Dr. Teller, who maintained that he and his colleagues had found a novel way to end the strategy of Mutual Assured Destruction (MAD) that has dominated superpower relations for more than a third of a century.

In July 1983, a few months after the ''Star Wars'' speech, Dr. Teller summarized his ideas in a letter to the President. Advances in nuclear-driven weapons, he wrote, ''by converting hydrogen bombs into hitherto unprecedented forms and then directing these in highly effective fashions against enemy targets would end the MAD era and commence a period of assured survival on terms favorable to the Western alliance.''

Dr. Teller's devices were known as third-generation weapons, their predecessors being the atom and hydrogen bombs.

What divided them was how to deal with the Soviet Union. For decades Dr. Teller had put more faith in technology than in diplomacy to protect the United States from the threat of nuclear war.

In February 1983, the two men met at the Livermore nuclear-weapons laboratory. Dr. Teller tried to win over Dr. Bethe by revealing the top-secret details of what Dr. Teller considered the ultimate technical fix to the arms race. This was the nuclear X-ray laser, a device that would be based in space and whose powerful beams were meant to shoot down Soviet missiles. As the bomb at its core exploded, multiple beams would flash out to strike multiple targets before the whole thing consumed itself in ball of nuclear fire.

''You have a splendid idea,'' said Dr. Bethe, complimenting Dr. Teller on the physics of the unusual device. But novelty was not enough for the Nobel laureate. Soon he helped organize opposition to the X-ray laser and its exotic brethren, arguing that a defensive shield could easily be outwitted by an enemy. All it would take were simple countermeasures.

''We need to try to understand the other fellow and negotiate and try to come to some agreement about the common danger,'' Dr. Bethe said in an interview. ''That is what's been forgotten. The solution can only be political. It would be terribly comfortable for the President and the Secretary of Defense if there was a technical solution. But there isn't any.''

''Bethe sees the future in a too-easy manner,'' Dr. Teller said in an interview. ''He was there at the birth of quantum mechanics, and he was there when we constructed the first atom bomb. Now he says there won't be anything new under the sun. Hasn't he seen enough new things?''

For decades Dr. Teller had searched for technologies that could defend the country from the threat of enemy H-bombs. ''It would be wonderful,'' he wrote in ''The Legacy of Hiroshima,'' his 1962 book, ''if we could shoot down approaching missiles before they could destroy a target in the United States.''

Technology at the time was too feeble for the job, but Dr. Teller warned that the West should be watchful lest the needed breakthroughs were made elsewhere.

''If the Communists should become certain that their defenses are reliable and at the same time know that ours are insufficient,'' he wrote, ''Soviet conquest of the world would be inevitable.''

His fear was unstated but clear. An aggressor with a good shield might be tempted to use his spear, confident he could deflect the weapon of his opponent.

It now supports about 120 graduate students every year and has assets of about $14 million. According to the foundation's directory, the weapons laboratory is the largest single employer of Hertz fellows and alumni, having at least 29 of them. The fellows at the laboratory, who work there while pursuing their doctorates, are some of the brightest.

According to a recent brochure, the foundation has an ''express interest in fostering the technological strength of America'' and ''requires all fellows to morally commit themselves to make their skills and abilities available for the common defense, in the event of national emergency.''

The foundation's president, Dr. Wilson K. Talley, is chairman of the Pentagon's Army Science Board and is a professor at the University of California at Davis/Livermore, a graduate school at the weapons laboratory whose $1 million facility was built with the help of Hertz funds. Asked if the foundation had been a catalyst in ''Star Wars,'' he replied: ''We've been supporting people for years all over the country in computer science, materials science and nuclear physics. We've attempted to be elitist. Only one out of 15 who apply get a fellowship. And those 15 have A-minus averages. So it's not surprising that some of the brightest brains in the Strategic Defense Initiative happen to be Hertz fellows.''

Dr. Teller was once ''coordinator'' of the foundation's fellowship project. That job is now held by Dr. Lowell L. Wood Jr., a protege of Dr. Teller's at Livermore. The foundation's address is a post office box in the nearby city of Livermore.

Three months later, the magazine Aviation Week & Space Technology carried an exclusive article that identified no sources but described the top- secret test in detail.

''The X-ray lasers based on the successful Dauphin test, when mounted in a laser battle station,'' it said, ''are so small that a single payload bay on the space shuttle could carry to orbit a number sufficient to stop a Soviet nuclear-weapons attack.''

In May 1981, Dr. George A. Keyworth 2d was named the President's science adviser. A nuclear physicist, he was intimately familiar with the X-ray secrets and had been strongly endorsed for the job by Dr. Teller.

Also in 1981, a group of influential scientists, industrialists, military men and aerospace executives began to meet in Washington, D.C., at the Heritage Foundation, a conservative ''think tank.'' Their goal was to formulate a plan for creating a national system of defense. Among them were Dr. Teller, Dr. Wood and such members of the President's ''kitchen cabinet'' as Joseph Coors, a beer executive; Justin Dart, a wealthy businessman, and Jacquelin Hume, an industrialist.

The group's top officer was Karl R. Bendetsen, once Under Secretary of the Army, later chairman of the board of the Champion International Corporation, and a long-time overseer of the Hoover Institution on War, Revolution and Peace. Since the 1940's he had known Dr. Teller, who in addition to his weapons work also held a post at Hoover. The group's second-in-command was Lieut. Gen. Daniel O. Graham, retired from the Army, once head of the Defense Intelligence Agency. All group members received security clearances so they could learn about and discuss secret details of new technologies and weapons.

But by late 1981 the group began to split over differing visions of how to carry out the task of space-based defense. Mr. Bendetsen, Dr. Teller and the Reagan 'kitchen cabinet' separated into a small group to investigate sophisticated proposals that would require much more research before being ready to use, while General Graham and his group, known formally as High Frontier, emphasized systems that could be built primarily from ''off the shelf.''

Another factor in the split, according to General Graham, was that Dr. Teller insisted on the inclusion of third- generation weapons powered by nuclear bombs. ''He wanted very much to leave in the nuclear options,'' the general said. ''The man is carrying a load and has taken a lot of abuse as the 'father' of the H-bomb. Now he wants to see nuclear technology turn out to be the answer in the opposite direction, to save the Western world.''

The split had vast implications in terms of Presidential access. Mr. Bendetsen and his friends visited the White House with ease. General Graham did not.

And this division went to the heart of a dispute that today haunts the Pentagon's search for a defensive shield - the rivalry between basic scientists and applied scientists. On one side are the national laboratories, universities and contractors that carry out basic research on such directed-energy weapons as lasers and particle beams. Systems based on their results might be decades away. On the other side are contractors who want to quickly turn dollars into demonstration projects and are pushing for quick deployment of prototypes.

The winners have tended to be the barons of basic research. An example can be seen at the Sandia National Laboratory, one of three facilities in the nation for the design and develop nuclear weapons. Based in Albuquerque, N.M., it is about to break ground on a $70 million center to investigate ''Star Wars'' technologies, both nuclear and non-nuclear. About 10 percent of the Strategic Defense Initiative's budget is devoted to the development of nuclear weapons.

Indeed, the recommendation taken to the President by Mr. Bendetsen and his group was to start a stepped-up program of advanced research rather than trying to create a defense with ''off the shelf'' technology. The first meeting occurred in January 1982. Dr. Teller was present.

''The President expressed great interest,'' recalled a source intimately familiar with the meeting. The conversation, he said, focused on directed- energy weapons that might be used to destroy aircraft as well as missiles. There was much talk of lasers. The group told Mr. Reagan that the Pentagon was experimenting with lasers that might have only limited capacity because their wavelength was too long.

The shorter a laser's wavelength, the more destructive energy it can pour onto a target. The laser that now holds the record for short wavelength is the X-ray laser.

The January 1982 meeting at the White House had been scheduled to last 15 minutes. It went on for an hour.

General Graham, denied access to the President, took his case to the public. In February he issued the High Frontier report, a 175-page book filled with a detailed description of the group's vision as well as color sketches of defensive battles in space.

In its forward, General Graham recalled the group's search for ''a technological end-run on the Soviets'' and said it had ''led inexorably to space.''

''The U.S. advantage in space is demonstrated in its most dramatic form by the Space Shuttle,'' he wrote. ''More fundamentally, the ability of the United States to miniaturize components gives us great advantages in space where transport costs-per-pound are critical. Today a pound of U.S. space machinery can do much more than a pound of Soviet space machinery. It also happened that the technologies immediately available for military systems - beyond intelligence, communication and navigation-aid satellites - are primarily applicable to ballistic missiles defense systems.''

In an interview, General Graham said he was personally able to deliver the recommendations of the High Frontier panel to Gen. John W. Vessey Jr., who soon after became the Chairman of the Joint Chiefs of Staff. ''He was pretty positive from the very beginning,'' General Graham said.

Although Dr. Teller had access to the President, it was access in which others controlled the time and agenda. His group met with the President five times in all - three times before before the speech and twice afterward.

White House sources said Dr. Teller got an additional, private meeting through the following incident. In June 1982 Dr. Teller taped a segment of the ''Firing Line'' television program, hosted by William F. Buckley Jr., and complained that he had been denied Presidential access.

''May I tell you one little secret which is not classified?'' Dr. Teller asked. ''From the time that President Reagan has been nominated I had not a single occasion to talk to him.''

When aired on national television, Dr. Teller's comment brought an invitation from the White House. He had a private meeting with the President in September 1982, according to White House sources, although Dr. Teller refuses to confirm or deny that he had any meetings with the President on ''Star Wars'' before Mr. Reagan's speech.

Also on the ''Firing Line'' program, Dr. Teller and Mr. Buckley discussed why someone might invent new weapons to counter the threat of Soviet missiles.

Mr. Buckley: ''I'm certainly not asking you to solve the problem of original sin. But we do know that somebody figured out how to take several hundred million tons of explosives and launch them in the Soviet Union and make them fall in the United States. Now, it is a challenge that would fall within the apparent competence of the same scientists who invented that to invent something that would frustrate that. The same people who invent fighter airplanes that get in the way - that sink submarines - are the same kind of people who invent submarines, right?''

Dr. Teller: ''You have explained a good part, an important part, of my own psychology.''

In the first two years of the Reagan Administration, the X-ray laser was a Government secret. No official was to admit that it existed. That silence was broken on Jan. 14, 1983, when the President's science adviser, Dr. Keyworth, gave a talk at the Livermore laboratory, where the device had been invented. There he praised the ''bomb- pumped X-ray laser'' as being ''one of the most important programs that may seriously influence the nation's defense posture in the next decades.''

In the early months of 1983, the pace of Presidential meetings and consultations over a national defense program began to quicken. Mr. Reagan again met with the Teller-Bendetsen group. On Feb. 11 the President met with the Joint Chiefs of Staff. Although that meeting was scheduled to focus on the MX missile, Mr. Reagan is said to have kept the discussion centered on defensive systems for half an hour.

Robert C. McFarlane, then deputy national security adviser, Dr. Keyworth and Mr. Reagan himself have all been credited with having written the crucial parts of the March 23 speech.

After its delivery, Dr. Teller hailed the President in a March 30 article written for The New York Times.

''Today, a wide range of good and ingenious technical plans, ranging from simple to extraordinarily complex, challenge the widespread opinion that practical defense cannot be obtained,'' he said. ''Mr. Reagan did not lightly accept the idea that these can be made to work. He wanted to know a vast number of details. He asked questions of his science adviser, George Keyworth, and of many other scientists, myself included. He then decided that something must and can be done.''

The President's speech took some of his advisers by surprise and was later criticized by Alexander M. Haig Jr., former Secretary of State. In a talk at the Livermore weapons laboratory in August 1984, he charged that the speech had been poorly timed and prepared.

''The White House guys said, 'Hey, boss, come on. You're going to make a big splash. Big P.R. You're going to look like the greatest leader in America. Get out there and give that speech.' And he did,'' Mr. Haig said. ''But the preparation had not been made. I know the aftermath the next day in the Pentagon, where they were all rushing around saying, 'What the hell is strategic defense?' ''

''What they came up with is a technical edge that looks totally pacific,'' said Dr. Jeremy J. Stone, director of the Federation of American Scientists.

''There's always been a school of thought that says we should try to challenge the Soviets with technology,'' said Dr. Sidney D. Drell, a Stanford University physicist and co-author of a study that disparages ''Star Wars.'' ''And this is clearly one way to do it.''

In general, critics say that ''technical edges'' have always tended to disappear, leaving the world less stable and filled with more weapons. They note that it took just a few years for the Russians to catch up to the United States in A-bombs, H-bombs and multiple independently targeted warheads.

Defenders of the President's plan deny that they are searching for a technical edge and say trying to defend the nation is feasible, morally sound and a rational alternative to the idea of mutual terror.

''I've listened very hard to the arguments of the critics,'' said Dr. Steven D. Rockwood, associate director for defense research programs at the Los Alamos National Laboratory, the birthplace of the atomic bomb. ''They're not technical, although the critics try to put technical clothing on them. They're theological or philosophical.''

Defenders point to some ''philosophical'' statements that suggest that nuclear weapons and the ''balance of terror'' have played a useful role in keeping the peace between the superpowers.

General Graham says such logic is faulty. ''It appears that adherence to MAD has preserved the peace or kept us from major conflict,'' he said. ''The reality is that we can continue to say that up until the day the missiles begin to fly.''

''We have begun research on a non-nuclear defense against nuclear attack,'' Mr. Reagan told a group of Nobel laureates and other scientists in February. ''You on the cutting edge of technology have already made yesterday's impossibilities the commonplace realities of today. Why should we start thinking small now?''

According to Pentagon officials, some of the reasons that nuclear-defensive weapons have lost their luster include: the existence of a treaty baring their pre-deployment in space; the time constraints of trying to quickly get them into space during an attack; the damage in space that exploding nuclear weapons would inflict on nearby satellites, and the paradox of trying to make nuclear weapons ''impotent and obsolete'' by means of a new generation of nuclear weapons.

Under the auspices of the Strategic Defense Initiative, billions of dollars are still earmarked to flow into the development of third-generation nuclear weapons, the X-ray laser among them. But Pentagon officials say these weapons are now seen as being useful mainly as anti-satellite and ''counter-defensive'' weapons. An X-ray laser, for instance, might be used to knock out Soviet defensive battle stations so American retaliatory missiles could get through.

But the X-ray laser, which had been envisioned as destroying Soviets missiles and thus, as Dr. Teller put it in his letter to the President, to ''end the MAD era,'' is no longer assigned the main job.

A lingering question no one can answer is whether ''Star Wars'' would have happened in the absence of the X-ray laser. Mr. Reagan was obviously ripe for the idea of strategic defense. And so, it seemed, was a variety of new technologies, Dr. Teller's among them.

''I can see how Edward was attracted to all this,'' said a scientific colleague of Dr. Teller's who has long known and respected him. ''The X-ray laser was elegant. It was beautiful and elegant. It was technically sweet, just like Oppenheimer said. But is Edward an engineer? No. Is he a systems designer? No. Is he a military planner? No.

''He was enthralled with the principle and rightly so,'' he said. ''The principle is in fact that beautiful. But he is not the kind of guy who ever got hooked on building things. His first H-bomb was the size of an apartment house. Edward is a physicist with a fantastic creative mind. He understands the beauty of a piece of music. But for God's sake, don't ask him to design a trumpet.''

By Wayne J. Biddle

Hidden in the rocky canyons of the Santa Susana Mountains outside Los Angeles is the nearest thing to a ''Star Wars'' laser base anywhere in the Western world. Its code-name is Sigma Tau.

''This is as close to weaponization and as far from the laboratory as you're going to see without full-scale development,'' said Bill Robinson, director of laser programs for the Rockwell International Corporation, which began Sigma Tau secretly for the Air Force in 1976.

Two years earlier on the same site, Rockwell used its own money to start building a high-energy laser called Rachel, which the corporation describes as the forerunner to ''Star Wars,'' or, as it is officially designated, the Strategic Defense Initiative, for which the Government is proposing to spend $30 billion in the next five years.

The Strategic Defense Initiative research grew out of a speech by President Reagan in March 1983 in which he proposed that scientists and engineers design a defensive shield to render nuclear weapons obsolete.

Until Mr. Robinson led a reporter on a tour recently, no one outside military circles had ever been permitted to examine the huge mountaintop site of Sigma Tau.

Part of Rockwell International's mission is to demonstrate how to build lasers whose resonators, a component that helps extract intense beams of light from chemical reactions, are compact cylinders instead of long, narrow tubes. The goal is to find ways of someday packaging such objects into as small a volume as possible, Mr. Robinson said, with the space shuttle cargo bay a convenient unit of measure.

Today, Sigma Tau and its support equipment take up acres of land, resembling a small oil refinery rather than a feasible space-based antimissile weapon. This is ''basically a battleship environment to test the physics,'' Mr. Robinson said, noting a 300,000-pound base-plate that helps keep the laser's lightbeam steady. The space shuttle's freight capacity into polar orbits over the Soviet Union is only about 35,000 pounds, by comparison.

Lifting the curtain of secrecy around Sigma Tau was part of access to ''Star Wars'' work at the commercial level recently granted by the Pentagon's Strategic Defense Initiative office and the military service branches. In a series of interviews with military industry engineers across the country, all of whom were allowed to speak publicly for the first time about their work, these were among the major points:

- The Reagan Administration's optimism about developing a defense against nuclear missiles is supported, in part, by years of industrial research and actual weapons-building. But the industry has only the most rudimentary engineering ability in many crucial areas.

- Assuming that the primary components of an effective antimissile system - lasers, rocket interceptors, sensors, computers and power supplies - can be reliably manufactured, putting much of this equipment into orbit around the earth and maintaining it there year after year represent additional challenges of uncharted dimensions.

- By bringing formerly diffuse antimissile programs under one administrative aegis, President Reagan has created not only a potentially valuable hothouse for new ideas but also a vulnerable target for critics, making some industry officials wary of long-term commitment.

From Bethpage, L.I., where engineers for the Grumman Corporation have been studying space-based radars for a dozen years, to Orlando, Fla., where the Martin Marietta Corporation is trying to push its 1960's-vintage missile interceptors into the next century, to the West Coast, where companies like Rockwell, TRW and the Boeing Corporation have been building lasers, power supplies and sensor devices for more than a decade, there is no doubt that ''Star Wars'' is far more than fantasy, or at least more than the political gambit that some have suggested it is.

Unlike their scientific colleagues at national laboratories like Los Alamos and Lawrence Livermore, however, the engineers are faced with having to make business decisions. At a time when activity on conventional military programs is already booming and highly trained technologists are in short supply, capitalism has lent a sobering dose of reality to the science-fictional promise of ''Star Wars.''

At Grumman, where profits have customarily come from building warplanes for the Navy, a small group of engineers has been steadily working on a type of radar antenna, called ''space-fed,'' that might offer the size and weight advantages necessary for operation in space. In the last decade, the Government has spent about $15 million on space-based-radar work at Grumman, with the company also investing some of its own money.

Although less glamorous than the big lasers that have given the Strategic Defense Initiative its popular sobriquet, radars that operate from satellites and that can create detailed images of thousands of targets simultaneously at great distances are a linchpin of any future antimissile system. Existing ground-based radars such as the elaborate network operated by the North American Air Defense Command have little technical relevance for such systems.

While conventional radars rely on a reflector dish or labyrinthine cable tubing to transmit and receive electronic signals, Grumman's space-fed array uses a flexible plastic membrane embedded with many tiny antennas that can be unfurled like a window shade. These antennas radiate radar energy from a solar- or perhaps nuclear-powered source at the end of an extended mast over the membrane, hence the term space-fed.

''This type of antenna is an order of magnitude less sensitive to structural deformations'' than radars like the powerful Aegis array developed by the Navy for ship defense, said Robert Mantus, a Grumman radar engineer. ''It's very lightweight, but it isn't delicate.''

Low mass would be a crucial advantage in enabling a radar satellite to perform evasive maneuvers in a combat situation, and the ability to withstand forces that could bend or damage it and still produce accurate signals is important for such antennas that must create precise images of targets as small as nuclear warheads.

''I don't think it's unreasonable that in 10 years you could do it,'' said John Diglio, director of the company's space-based radar program, of putting an operational space-fed antenna in orbit. ''Technology-wise, many of the key points have been demonstrated.''

But the Grumman antenna, he said, would have to be the size of several football fields to provide the resolution needed to track warheads. The largest device built and tested so far is only 10 feet square.

''To say it's simple would be incorrect,'' said Mr. Diglio, of expanding the model to a full-sized ''Star Wars'' antenna. ''One could go out and build just an antenna - it wouldn't be much of a problem. But one wants to develop a whole satellite that deploys, possesses all the structural and survivable properties.''

As in other areas of space weaponry development, it is this process of scaling up that remains an engineering quandary. The academic science and technology needed to conceive a prototype may exist, but the path toward real-life hardware is for the most part unexplored.

At Martin Marietta, engineers hold the advantage of a corporate history that includes having actually built and tested a full-scale antimissile interceptor for the Army. Called Sprint, after its ability to reach high altitude targets only seconds after launching, the missile was first launched successfully in 1965, less than three years after design studies began. It was retired by the mid-1970's, however, along with the rest of the nation's Safeguard anti-missile system, which was judged to be too costly and ineffective.

''We have just completed a seven- month concept definition'' of new interceptors, said Joel Strickland, technical director of Martin Marietta's effort to win an Army contract for interceptor development. ''We approached it with a little bit of the same fear and trembling that was in the introduction to Sprint.''

''None of us believes that this is something we have to have an act of faith to sign up for,'' he said.

But ''the problem is not duck soup,'' he added. ''We are asking this to go faster, and the real nut is non-nuclear engagement.''

By non-nuclear engagement, Mr. Strickland referred to the fact that unlike Sprint, which carried a neutron bomb to destroy incoming targets within the earth's atmosphere, the proposed ''Star Wars'' interceptor, a self- propelled rocket, would rely on a conventional explosive so as not to black out its tracking radars. The difference in guidance accuracy is formidable: Sprint needed only to arrive several thousand feet away from its target, but the new interceptor must approach within several yards at ranges far greater than Sprint's and at twice the speed.

''That has yet to be demonstrated,'' Mr. Strickland said, ''and there are people who won't believe it until it is.''

Non-nuclear engagement of a primitive sort was demonstrated last summer, when an Army missile successfully intercepted a dummy warhead above the atmosphere. This was essentially a laboratory experiment, albeit with full-scale hardware, in that the trajectory of the warhead was known in advance and little maneuverability was required.

The Air Force's anti-satellite, or ASAT, weapon is also a non-nuclear device. Launched from an F-15 jet fighter, it ascends directly toward its target in low orbit and homes in on the faint heat emitted by a satellite against the cold background of space. The homing mechanism, developed by the LTV Aerospace Company, relies on infrared telescopes and 56 computerized thruster rockets to steer toward the target. The Air Force recently had to postpone testing the weapon because of difficulties with just two of the thrusters.

Martin Marietta's Orlando division is also drawing upon its experience in building so-called smart projectiles, like the Copperhead guided cannon shell. These projectiles, which can theoretically home in on their targets - with the aid of sophisticated heat sensors, for example, instead of just being lobbed like ordinary artillery shells - are crucial to the eventual success of some principal ''Star Wars'' weapons. Copperhead itself was a troublesome program for the company, however, and has been widely criticized as an ill-conceived weapon.

''In our case, we're hit-to-kill,'' said Joseph Casalese, who is studying smart projectiles and ways to launch them for Martin Marietta. ''Our miss distance is zero.''

The device most frequently mentioned for shooting smart projectiles is called an electromagnetic railgun, which so far exists only in primitive laboratory models. Instead of firing shells with a chemical explosion, the rail gun would use tremendously strong magnetic fields to fling them along metal guides and out through frictionless space.

''You have to accelerate greater than any other weapon produced in this country, on the order of hundreds of thousands of times greater than the force of gravity,'' Mr. Casalese said. The Copperhead shell, by comparison, can withstand forces of only about 9,000 times gravity.

''There are some basic physics of materials that you may get into when you start talking about a couple of hundred thousand G's at launch,'' Mr. Casalese said, adding that the shell's micro-miniaturized electronics would also have to withstand the intense magnetic fields, which could induce damaging jolts of current.

''I think most people will admit that there are severe logistics problems in doing a space-based weapons system'' of this kind, he said.

Yet with all its uncertainties, the ''smart'' projectile could be the easiest part of a rail-gun system to develop, he said, compared with the launcher itself, for which there are no workable military precedents.

At the University of Texas, an experimental rail gun named ''Gedi'' sits in a high-ceiling laboratory crammed full of electrical generators and equipment. It would have been named ''Jedi,'' like the movie, but that name is covered by copyright.

The gun, which is hardly a weapon, is a faint hint of what might come in the future. A few dozen feet long and less than an inch in diameter, it can fire pellets weighing 85 grams to high velocities, but not repeatedly. Smart projectiles foreseen by Martin Marietta engineers, by comparison, would weigh several thousand grams.

With new financing from the military, the Texas researchers are getting ready to build Gedi II in a new seven- story-tall building. All together, with its special detectors and equipment to measure the speed and characteristics of projectiles, the new ''gun'' will measure over 130 feet long.

''I think advances in power supplies and launchers in the next 25 years are going to be mind boggling,'' said William Weldon, a scientist at the university's Center for Electromechanics. ''The biggest worry I have is hitting multiple targets.''

Of all the contractors at work on antimissile weapons technology, Rockwell's Rocketdyne division in Los Angeles is among the most deeply involved. Over all, the corporation's ''Star Wars'' work was worth about $50 million last year, most of that money coming from Government contracts.

'' 'Star Wars' didn't all of a sudden come upon us,'' said R. D. Paster, Rocketdyne's vice president of advanced programs. ''Rocketdyne has been involved in technology in that area for over 10 years.

Mr. Paster said that from an engineering standpoint, ''we probably know more about how to do the job with electromagnetic launchers and can foresee the types of problems we'll have than we can with a directed energy system.''

He noted that directed energy devices, including lasers, ''still have a lot of physics to work out.''

Chemical lasers, like Sigma Tau, get their energy from combustion of fuels similar to those used in rocket engines. Large portions of the energy produced by these chemical reactions are lost as heat. But significant amounts can be extracted in concentrated beams of ''coherent'' light, which might be compared to ocean waves all moving in perfect unison. A system of mirrors and resonant chambers are used to pick up the energy the way a violin's body picks up the vibration of its strings.

Lasers are envisioned mostly for use in space, since the atmosphere can absorb their energy or disrupt the light-beams in various ways.

Sigma Tau's fuel produces relatively low-energy infrared light-beams, compared with what would be needed to destroy enemy missiles. Indeed, chemicals that would create the high energy beams needed for weaponry are as yet unproven, though Mr. Robinson said that this ''Holy Grail is almost here.''

Some of Rocketdyne's long experience in building large rocket engines may be applied to electromagnetic launchers, as well as to chemical lasers.

''It turns out that the amount of heat that goes into the rails is equivalent to the heat that goes into our space shuttle main engine nozzles,'' Mr. Paster said. Learning how to cool the space shuttle engine contributes to solving the problem of keeping the rail gun from melting.

Rockwell is also developing a source of electrical power for use in space, one of the most critical yet little discussed aspects of the ''Star Wars'' dream.

''We're in a situation where you might have 40 spacecraft, different types that you would want to join to, and it's got to meet the special needs of each one,'' said Bob Anderson, program manager for space nuclear power. Weapons generally require huge pulses of electricity, whereas radars or computers run steadily at a lower level, rather like home appliances.

''Power is definitely an enabling technology for many of the weapons,'' Mr. Anderson said. ''The total power area is not solved by any means, especially in the very high powers and high currents. There we're not yet into as many engineering decisions as we are in what we call 'hotel power,' which keeps all the backup capability going - data processing, cooling, et cetera. That area is very touchy.''

To help solve the power problem, the Pentagon announced the creation last week of a $19 million, four-year research program at a consortium of five universities. Lieut. Gen. James Abrahamson of the Air Force, director of the Strategic Defense Initiative, said the group would ''address critical problems associated with the issues of non-nuclear space power.''

Rockwell's main competitor in the chemical laser field is the TRW Corporation, which is working on two large devices of the same general class as Sigma Tau. One, called Miracl, was the first laser to produce more than a megawatt of light energy.

In theoretical discussions, laser weapons of about 25 megawatts output are assumed. Miracl, whose resonator is not of the cylindrical design, was originally studied by the Navy in a ship defense program, but two years ago Congress cut off its appropriation. Now it has been revived and moved from San Juan Capistrano, Calif., to White Sands, N.M., where it will be tested in combination with a pointing and tracking mechanism.

The other device, known as Alpha, is only six months past the ground-breaking stage of construction, according to Bob Walquist, TRW vice president and program executive on Strategic Defense Initiative projects. Mr. Walquist said Alpha would be about the same power level as Sigma Tau and would also use the cylindrical design.

This design is considered attractive because it makes easier the venting of exhaust from the device's chemical reactions without creating counteracting forces that would cause a laser satellite station to career out of control. Earth-based lasers, which are also under experimental development, would obviously not have such a problem.

The X-ray laser, which was developed at the Lawrence Livermore National Laboratory in California and which is triggered by a nuclear explosion in space, was the device that initially gave scientists confidence that a missile defense system could be deployed in space. The Reagan Administration, however, in recent months has emphasized the non-nuclear nature of its proposed defense system. In part because of the necessary nuclear explosion, the X-ray laser has fallen out of favor as the laser of choice.

In addition to the chemical and X-ray lasers, there are several other types being studied at Rockwell and TRW, but they are considered to be far more technically exotic. So-called free-electron lasers, for example, are powered by electricity instead of chemical reactions. Their enormous atomic-particle accelerators fire electrons that are then tricked into producing coherent light. Current models are so large that combat applications are extremely uncertain.

Particle beams are also often mentioned in the directed energy category of possible ''Star Wars'' weaponry. These are not lasers. Instead of sending intense light energy toward a target, they would fire streams of atoms or subatomic particles at nearly the speed of light. In contrast to a laser, which destroys or damages its target by radiating its surface with light, particle streams would actually penetrate a target, disrupting its electronic circuits, inflicting structural damage, or perhaps detonating chemical explosives meant to trigger atomic reactions in a warhead.

Particle-beam technology is generally regarded as even more rudimentary than laser weaponry, and most of its design is being undertaken not by industry but by Government laboratories. At Lawrence Livermore, scientists are at work on a $50 million machine called the Advanced Technology Accelerator, which stretches for hundreds of yards in a shallow, dry valley. The site was chosen so the surrounding hills could provide shielding in case of an accident.

In addition, the Los Alamos lab in New Mexico is building a particle- beam accelerator known as White Horse, and the Sandia National Laboratory in New Mexico is using particle technology developed in the search for fusion energy in an attempt to create particle beam weapons.

Perfection of new supercomputers is another requirement of ''Star Wars.'' Vast, elaborate and second-by-second tracking, aiming, firing and coordination of various phases of the whole system would, of necessity be handled by the most sophisticated of computers. To do the job, computer software containing on the order of 10 million instructions would have to operate flawlessly. By comparison, the final nine minutes of a space-shuttle launching, when all operations are under automatic computer control, take about 88,000 instructions.

TRW is involved in this area, along with such well-known computer companies as IBM and Honeywell, in studying how to command and control a vast antimissile network whose entire battle engagement would last less than 30 minutes. ''The 10 million lines of code is something that 10 years ago would have been impossible, today is impractical, but tomorrow with the development of programming aides is going to be within the realm of possibility,'' Mr. Walquist said.

As for the overall system, however, he was not as optimistic. ''Right now,'' he said, ''I think the whole area of what is going to be done in response to S.D.I. is still really up in the air.''

TRW and nine other companies recently began so-called architecture studies of how the entire antimissile system might look , which will be followed by cost analyses.

''Until the architectures get looked at in a little more detail,'' Mr. Walquist said, ''I sort of go home at night and worry about what you're going to do in all these phases.''

Although major aerospace companies have already mustered some of their resources for President Reagan's Strategic Defense Initiative, there is a pervasive sense in the industry of waiting to see how Congress and the public treat the idea.

So far, the companies have devoted only fractions of their total workforce to S.D.I. Martin Marietta's Orlando division, for example, has about 100 people out of 11,000 employees on work related to the Strategic Defense Initiative. Even at TRW, which is considered a major ''Star Wars'' contractor, the fiscal value of its projects is only about $100 million, compared with well over a billion dollars worth of other military work. Moreover, many of these projects existed long before President Reagan's speech in March 1983 created a national priority.

Yet the business of the engineers is to make things work, so they carry a ubiquitous optimism in the face of admittedly horrendous technical problems.

''As the idea gets dropped on the table, everybody empties out their file cabinets and conjures up ideas - 'Star Wars' - and it's so easy for the critics to shoot it down, it's totally immature,'' said Michael I. Yarymovych, Rockwell's vice president of advanced systems development and a former chief scientist for the Air Force. ''But as time goes on, you'll see the critics becoming more and more confused and quiet. Because as time goes on, people will start coming in with new thoughts that are totally different from the old ones.''

By Charles Mohr

The Soviet Union is approximately equal to the United States in basic research on directed energy, like lasers and subatomic-particle beams, that would be required for a broad land- and space-based missile defense system, according to Pentagon reports.

But the Russians are said to trail badly in the technology that would be needed to turn such energy beams into workable weapons.

High Reagan Administration officials publicly express a belief that a United States drive to design a space-based missile system, as a defense against nuclear attack, will eventually force the Soviet Union to give up its reliance on offensive land- based intercontinental ballistic missiles and build a similar defense system of its own.

These officials say the result of the American effort, made through its Strategic Defense Initiative, more commonly called Star Wars, would be a more stable nuclear standoff.

In the view of several other experts on Soviet policy and weapons technology, however, the Soviet Union may instead multiply its offensive missile force in the hope that it can saturate and overwhelm the proposed United States defensive shield. The Russians will also probably explore technologically simple and inexpensive methods of overcoming a ''Star Wars'' defense, the analysts say.

In private, some Government authorities agree that both the Soviet development and the American Strategic Defense Initiative are more likely to reach a result opposite from that intended: by encouraging an offensive arms race, bringing about the death of the 1972 treaty limiting antimissile defenses and prompting a shift toward a more hostile, hairtrigger relationship between the two powers.

Interviews with experts on the Soviet Union both in and outside the United States Government and a review of their writings and public statements shows a general belief that, eventually at least, the Soviet Union may also seek to build a defensive umbrella against intercontinental missiles.

In the next few years, however, some experts say, they believe the Soviet Union will probably take few dramatic or visible military steps to counter the professed intention of the Administration to build a new and complex strategic nuclear defense.

The Russians already have by far the most extensive strategic, or long- range, defense system in the world. But it is known to be porous. It includes an air defense of 10,000 surface-to-air missiles and thousands of interceptor aircraft and a relatively primitive and rudimentary anti-ballistic missile defense in the Moscow area.

Defense Department officials say they do not believe these defenses could prevent penetration of the Soviet Union by low-flying bombers and cruise missiles or prevent a crushing blow by nuclear missiles. Nonetheless, they say they are worried that the use of mobile radars and ''upgraded'' surface-to-air missiles could be used in an effort to provide a nationwide antimissile network now prohibited by treaty.

Speaking four days after President Reagan outlined his own hopes in March 1983 for a defense that would render nuclear weapons ''impotent and obsolete,'' Yuri V. Andropov, then the Soviet leader, said, ''Should this conception be translated into reality, it would in fact open the floodgates to a runaway race of all types, both offensive and defensive.''

Sayre Stevens, a former deputy director of the Central Intelligence Agency and a consultant on national security matters, said of the Administration's goal of shifting from a strategy of deterrence based on retaliatory offensive power to one of defense, ''I don't quite see how you get from here to there.'' And he predicted a period of strategic uncertainty.

Stephen M. Meyer of the Massachusetts Institute of Technology and a Defense Department consultant on Soviet military policy, said, ''It's not going to be a race between our 'Star Wars' and their 'Star Wars,' but a race against our system and their efforts to overwhelm or neutralize it.''

An increasingly frequent Administration contention is that the Soviet Union is ''doing more than we are'' in the exotic technologies needed for a nearly leak-proof and advanced defense.

Richard D. DeLauer, a former Under Secretary of Defense for Research and Engineering, told Congress that although the Soviet Union ''equals'' the United States in directed energy research, it ''lags in other technologies that are crucial'' for missile defense.

He added, ''We are ahead in computers, optics, automated control, electro- optical sensors, propulsion, radar, software, telecommunications and guidance systems.''

The area in which the Soviet Union leads the United States is in large rockets with great throw-weight - the capacity to lift and propel great weight. But for lifting such things as fuel and components for space battle stations, the United States space shuttle is regarded as more useful than large rockets.

High-speed computers will also be needed to manage a ''Star Wars'' defense.

''The United States is working to transcend fourth generation computers, while the Soviet Union is still struggling to master the third generation,'' said John E. Pike, a space policy analyst of the Federation of American Scientists, a private group that studies policy problems arising out of science.

But, despite an inferior technology base, the Soviet Union has always managed to match any major United States weapon innovation from early fission bombs to multiple warheads on missiles and high missile accuracy. The catch-up period has usually been shorter than American policy makers expected.

Statements regarding Soviet research and possible Soviet advantages are often difficult to check. Much of what is known about Soviet programs involves extrapolation from photo reconnaissance and electronic surveillance by American satellites.

The Soviet Union has what is believed to be two large ground lasers at Sary-Shagan in Kazakhstan, as well as a vigorous research program in particle-beam acceleration. Almost all experts, however, describe the lasers and programs as basic research and not active weapons development programs. Pentagon documents speak only of ''possible'' military applications.

''What we can measure, in fact, is mostly such things as floor space, probable electrical power consumption and so forth,'' Mr. Pike said. ''For example, we know nothing about laser tube life or reliability.''

A United States Government expert agreed, saying, ''We know nothing about beam resolution and other technical factors that would make a laser an effective weapon.''

A half-dozen officials in the Pentagon and the C.I.A. said intelligence about Soviet efforts was scanty and ambiguous.

Mr. Pike and Mr. Meyer used identical language in saying that American analysts tended to measure ''input rather than output,'' because they are forced to do so. ''The real question,'' Mr. Meyer said, ''is what the Soviets are getting out of it.''

The Soviet Union has been committed to a military doctrine called ''damage limitation,'' which has not until now been embraced by United States officials.

A belief in the usefulness of limiting nuclear damage has meant that the Soviet Union has historically been willing to put into place - and to expend large amounts of money and manpower for - marginally effective military systems that clearly could not protect the nation from nuclear devastation.

In the 1950's, for instance, the Soviet Union built a large fleet of interceptor aircraft meant to shoot down American bombers, but the interceptors could operate only in daylight and clear weather.

The Soviet antiballistic missile defense around Moscow is another example. Although Moscow was permitted by treaty to build 100 ABM launchers, it constructed only 68. A wide range of United States Government and non- Government analysts say they believe the actual protection provided against a huge United States strike is close to zero, but the Soviet Union did not dismantle its system as the United States did in the 1970's.

According to intelligence reports, the Soviet Union is now upgrading the Moscow ABM network with SH-04 and SH- 08 rocket interceptors that are much faster than the original Galosh rockets, although still slower than American Sprint rockets developed more than a decade ago.

The increased speed of the interceptors would apparently permit them to engage United States warheads after the warheads had re-entered the atmosphere, which would strip away the cloud of American decoys. This ''atmospheric sorting'' of targets could make the system somewhat more effective than the Galosh rockets, which intercept outside the atmosphere.

The Soviet Union has also made observable advances in phased array radars, which are steered electronically. Mechanically steered radars of the past are regarded as almost useless against a large swarm of warheads. But the Russians still trail in radar technology.

One Pentagon fear is that comparable improvements that permit tracking and engagement radars to pick up targets with low radar cross-sections - which is to say, American warheads - and to make radars mobile or transportable will bring closer the possibility of a nationwide ballistic missile defense. American monitoring of the new generation SA-12 surface-to-air missile tests indicate that they have some potential antimissile use, experts said, and could possibly be incorporated into a defense system.

Several other experts tend to agree with Mr. Meyer that Soviet policies regarding weapons development and deployment are different from those of the United States, and that if a true ''race'' develops the Russians are likely to be first into the field with rudimentary weapons.

''They have always been willing to field systems that did not work and then tinker with them through model changes and design innovation,'' Mr. Meyer said.

He said he believed the present ''operational'' ABM system was only now beginning to approach the effectiveness of American technology abandoned 10 years previously.

Mr. Meyer even predicts that if the Strategic Defense Initiative provokes unlimited competition, the Russians ''will be the first in space with a laser.''

He added that ''it won't be an effective weapon'' because the Russians would still face the daunting problems of finding targets and pointing and tracking, which are far from solution by superior American technology. ''But it will be a laser,'' he said, ''and it will drive Congress and officials here crazy.''

By Philip M. Boffey

The weapons envisioned for President Reagan's defensive shield against ballistic missile attack could be used with devastating effect offensively, according to many supporters and critics of Mr. Reagan's program.

The President's Strategic Defense Initiative, known popularly as ''Star Wars,'' would not use weapons of mass destruction, like the current nuclear arsenals, that could obliterate tens of millions of people, the experts agree.

But the same experts, in government, industry and the universities, say the proposed defensive system, if it is actually built and deployed at full strength, could serve several major offensive functions, including these:

- It could be used as a defensive adjunct to an offensive nuclear attack, allowing nuclear-armed missiles to be launched in an offensive strike while the defense is held in reserve to cope with any retaliatory strike, according to arms-control experts.

- It could attack and destroy enemy space satellites, which are generally far easier targets than the ballistic missiles the system would be designed to intercept, according to experts assembled by the Congressional Office of Technology Assessment. Satellites have become an increasingly important part of the military systems of the United States and the Soviet Union.

- It might even be used, some experts believe, in lightning-fast strikes from space against relatively ''soft'' ground targets, such as airplanes, oil tankers, power plants and grain fields, causing instantaneous fires and damage that, in the words of John D. G. Rather, a laser expert and ''Star Wars'' proponent, could ''take an industrialized country back to an 18th-century level in 30 minutes.''

There is even mild concern among some military experts that the system might ultimately prove able to destroy the concrete and steel silos that protect missiles underground, thus providing a first-strike weapon that could disable an opponent's missiles before they could be fired.

Although an overwhelming majority of experts consider that possibility extremely remote and easy to defend against, the Air Force Ballistic Missile Office at Norton Air Force Base in California is taking no chances: It has solicited proposals for a study to determine whether space weapons or other non-nuclear weapons might, in fact, be able to disable a missile in a hard silo.

The offensive uses would not be unique to the kind of weapons that will be explored under the Strategic Defense Initiative. If the Soviet Union should deploy a similar defensive shield, it, too, would almost certainly have the same offensive potential. The possible offensive uses of the proposed system have so far received only passing attention in the debate over Mr. Reagan's proposal. But the ambiguity between defensive and offensive weapons is beginning to cause concern among some of the scientists who are strong proponents of a better defense, as well as those who oppose the general goals of the Strategic Defense Initiative.

''I've been thoroughly aware of the problem for years,'' said Dr. Rather, vice president of the Kaman Aerospace Corporation, who has often testified in Congress in favor of a defensive system.

''Anything that involves large amounts of energy can be used for good or evil purposes,'' Dr. Rather said. ''A system of space battle stations designed to stop a nuclear attack also may have the potential to attack selected targets in space, in the atmosphere or down on the surface of the earth.''

He said the possible misuse of a defensive system for war-making purposes is ''something that has to be thoroughly studied and dealt with'' before such a shield is deployed.

But Edward Teller, a nuclear physicist with close ties to the Reagan Administration, said the Strategic Defense Initiative was ''unequivocally defensive and not offensive.''

Dr. Teller said he hoped new weapons could be designed strong enough to ''destroy the vulnerable, flimsy structure of a missile in the boost phase.'' But he said such weapons would almost certainly be ''completely helpless against silos'' and would probably have great difficulty finding and tracking ground targets, which could be more readily destroyed by existing weapons.

''To use this expensive system to accomplish something as pedestrian as that, something that could be accomplished much more easily by methods already available, what kind of sense is that?'' Dr. Teller asked.

At this point, of course, no one knows whether an effective defense can be built or what it would look like. The Strategic Defense Initiative is a research program designed to investigate a range of possibilities for disabling Soviet missiles that are launched against the United States. The study will investigate weapons such as high- speed projectiles and futuristic laser beams or particle beams that might be directed at Soviet missiles and warheads at all points along their flight paths, from the boost phase through the release of the warheads to the terminal phase, where the warheads plunge back into the atmosphere toward their targets.

The new defensive weapons might be based in space on hundreds of special platforms, or popped up into space at the first sign of attack, or based on the ground to fire upward. Depending on which weapons are ultimately selected and where they are based, the system could possess a range of potential offensive uses.

The most obvious one, recognized by both proponents and critics of the system, would be as a defensive adjunct to a nuclear attack. Some arms-control strategists fear that a nation that possessed a defensive shield, however imperfect, might be tempted to launch a first strike against its enemy, secure in the knowledge that the shield could knock down a ragged and uncoordinated retaliatory strike.

American officials stress that the United States, even with a defensive shield in place, has no intention of launching an unprovoked attack on the Soviet Union. But Mr. Reagan acknowledged, in his speech on March 23, 1983, announcing the program, that defensive systems could raise fears of an attack.

''If paired with offensive systems,'' he said, ''they can be viewed as fostering an aggressive policy, and no one wants that.''

''Whatever weapons are useful in an antiballistic missile role are even more useful in an anti-satellite role,'' said Wolfgang K. H. Panofsky, director of the Stanford Linear Accelerator Center at Stanford University in California, who is an expert on beam weapons and a critic of the President's program.

A workshop of experts brought together by the Congressional Office of Technology Assessment concluded last year that any effective defense against ballistic missiles ''is an even more effective anti-satellite weapon'' because ''satellites are much easier to destroy'' than missile warheads.

Satellites are more fragile than missile warheads, far fewer in number, and situated above the distorting and blunting effects of the atmosphere. These atmospheric effects make it difficult to hit missiles in the initial stages of their flights. Satellites also follow predictable orbits for months or years and can thus be targeted at leisure, whereas ballistic missiles would probably be launched without warning and would have to be destroyed in minutes.

As an example of the close correspondence between different weapon technologies, the Union of Concerned Scientists points out that the anti-satellite weapon now being developed in the United States exploits homing-vehicle technologies that were originally developed by the Army for use against ballistic missiles.

The more futuristic technologies under consideration, such as lasers and particle beams, would probably be able to destroy satellites long before they could destroy missiles, according to many scientists. Indeed, George A. Keyworth 2d, the White House science adviser, proposed in October 1983 that one of the earliest goals of the new defensive program might be to demonstrate the effectiveness of a laser not against missiles, but rather ''powerful enough to act as an anti-satellite weapon'' at ranges as great as 22,000 miles.

The X-ray laser, which would be powered by a nuclear explosion in space, could well become a premier anti-satellite weapon, according to top Pentagon officials, who add that it would thus become usable in knocking out Soviet space battle stations of the future. Although Administration officials are no longer publicly emphasizing the bomb-pumped laser as the centerpiece of ''Star Wars,'' research on it is nevertheless forging ahead.

Although there is little dispute among experts that a defensive system has offensive potential against targets in space, there is considerable disagreement whether the system would make a feasible and likely weapon against targets on the ground or in the lower atmosphere.

Attacking such targets would not be easy. Many of the technologies under investigation for ballistic missile defense have limited abilities to penetrate the atmosphere. Particle beams, for example, dissipate when they collide with other particles in the atmosphere. The X-ray beams emitted by one class of laser weapons are unable to reach very far toward earth. And many of the high-speed projectiles that might be used to destroy missiles by the impact of collision would probably burn up in the atmosphere long before reaching the ground.

But the proposed defensive system, if it works well, will have to have some weapons able to hit ballistic missiles shortly after launch, when they are still in the atmosphere. American military officials are also hoping to find weapons that can disable low-flying cruise missiles and bombers. Nobody knows if they will be successful. But if they can do that, many experts say, it should not be much more difficult to increase the range slightly and shift the aim to hit ground targets.

In principle, at least two of the weapon systems under investigation should ultimately be able to reach the ground from outer space.

High-speed projectiles, if made large enough and durable enough, could presumably be sent to collide with surface targets, smashing them to bits by the force of impact.

And optical lasers, which focus narrow beams of intense, hot light on their targets, should be able ultimately to burn targets on the ground. The so- called excimer laser, for example, will almost certainly be able to cross through the atmosphere. Under one proposed basing plan, the laser would sit on the ground and fire its beam all the way up through the atmosphere to mirrors based in space, which would redirect the beam back down toward ballistic missiles taking off.

Some experts believe that such lasers could provide an awesome instrument for surgically precise attacks against ''soft'' targets. Dr. Rather, a proponent of a space-based defense, wrote an article in 1982 saying a country that was the sole possessor of space lasers would have ''the longest 'big stick' in history,'' nothing less than ''the capability for unilateral control of outer space and consequent domination of the earth.''

Dr. Rather said such lasers could potentially ''deliver devastating non-nuclear strikes to high-value targets anywhere on the earth's surface, in the air or in space at the speed of light, from ranges of thousands of miles, with no collateral damage to adjacent civilian populations.''

Key targets, he suggested, might include oil tankers on the high seas, oil tanks on land, key power transformers, military vehicles and even troops, who might be blinded by laser light.

Other experts have suggested that fires might be started in grain fields and storage bins, thus starving a country into submission, or that flammable structures might be torched the length and breadth of a country to spread havoc.

In a recent interview, Dr. Rather said any defensive laser system hot enough and fast enough to destroy 1,400 ballistic missiles in a few minutes as they are boosted from the earth could almost certainly be designed to ''burn down through the atmosphere and easily kill an airplane or cruise missile or surface target, because these are essentially sitting ducks.''

Richard Garwin, an I.B.M. physicist opposed to the proposed defensive system, agreed that lasers of sufficient power could presumably ''shoot down airplanes or set millions of fires simultaneously all over the Soviet Union.''

And Henry W. Kendall, chairman of the Union of Concerned Scientists, which opposes the ''Star Wars'' proposal, mused at a recent breakfast meeting with reporters that lasers might also be used for ''selective assassination,'' perhaps picking off a whole row of top Kremlin officials watching the annual May Day military parade.

But such feats would have to be carried out in good weather. Clouds block the laser light from reaching the earth. And finding targets that move, like planes and cruise missiles, could be extremely difficult, especially if the new ''stealth'' technologies are used to hide the target from radar and other sensors. Moreover, scientists are still a long way from creating lasers powerful enough to serve as effective weapons.

Even if attacks on ground targets became technically feasible, many experts doubt that they would make much practical or military sense. Joseph A. Mangano, former deputy director of beam-weapons research at the Defense Department's Advanced Research Projects Agency, scoffed at the idea that space lasers would ever be an efficient and cost-effective way to destroy ground targets. ''One fire truck could hold off a space laser for a long time'' by simply spraying water on the hot spot, he said.

''You wouldn't build a laser for an offensive weapon,'' he added. ''It would be much more cost effective to send a bomb.''

But Dr. Rather countered that if a laser system was already built and deployed for defensive purposes, then the added cost of using it for offensive purposes might not be great. ''It might be the most cost-effective weapon,'' he suggested. Moreover, if it was urgent to destroy many targets almost instantaneously, he said, then laser weapons would be the best choice for the job.

The most devastating offensive use of space weapons would be for a first strike against ''hardened'' military targets, particularly the concrete-and- steel silos that house missiles on the ground. Most experts believe that this task would be formidably difficult, even impossible. The silos of both superpowers are built to withstand the enormous pressure and heat of a nearby hydrogen bomb explosion. Although a laser beam could, in principle, deposit a lot of energy on a silo, much as a magnifying glass can concentrate sunlight on a small spot, most experts doubt that laser light could cut through a silo cover or weld it shut.

''There is no prospect that a laser could could take out a silo, none whatever,'' said Dr. Kendall. ''Silos are designed to withstand nuclear bursts a few thousand feet away. No little itty- bitty laser is going to do anything to a silo designed for that.''

It would also be very easy to protect silos from laser attacks, many experts say, simply by covering them with materials to absorb or deflect the laser light.

A more formidable threat to silos might be ''kinetic energy'' weapons that rely on high-speed impact to smash their targets.

In principle, a suitably shaped piece of tungsten, uranium or other heavy metal could be fired from space at a silo or other hard target, possibly causing more damage than anything else except a direct nuclear hit. If the launching platform was in low earth orbit, the chunk of metal would reach its target faster than an intercontinental missile.

But American experts have studied the threat of offensive weapons in space for years and have always concluded that intercontinental missiles launched from earth would be more accurate and more reliable than anything dropped from space. Moreover, the kind of high-speed projectile useful against hard stationary ground targets would probably differ considerably from the projectiles that will be designed to intercept fast-moving missiles and warheads.

Supporters of the Strategic Defense Initiative stress that whatever offensive uses it may have are nothing like the enormous destructive power of nuclear weapons.

''These are not weapons of mass destruction which can take out a city and 2 or 3 million lives in 10 microseconds,'' said Lieut. Col. Michael Havey, the specialist on defensive systems for the White House Office of Science and Technology Policy.

''The S.D.I. weapons are precision weapons that destroy only precise targets,'' Colonel Havey said. ''They would not make good first-strike weapons because they could not take out the other side's cities, factories and people fast enough. These are weapons which kill weapons.''

Dr. Teller said: ''We are talking about defensive weapons, instruments of very high accuracy, which are directed against the instruments of attack only after they have been launched, not while they are in their silos. That is the only distinction I want to emphasize.''

By Philip M. Boffey

President Reagan's proposal for a vast system of space defense against ballistic missiles appears to be gaining strong momentum, even as members of Congress and experts outside the Government ask whether it is hurling the nation onto a new strategic course before the future implications can be fully considered.

Critics fear that the President's search for a defense that would render nuclear weapons ''impotent and obsolete'' will fail and yet is already driving the world's military competition in new directions.

Although the Soviet Union is believed to be substantially behind in the technology needed to put effective weapons in space, its leaders have said privately that they will have to accelerate their own research in this area. The Russians have said publicly that they will expand their production of offensive weapons in response to President Reagan's plan.

Experts on strategy disagree sharply on whether the world will become safer or more dangerous as this new missile-defense research program goes forward.

Top officials of the Reagan Administration now say that next Tuesday, when arms talks open in Geneva, the United States will try to keep a focus of discussion on how the two superpowers could put space defense systems into effect - not on whether research and development programs could or should be limited in any way.

In Congress, the proposed new defensive system and its potential implications are raising questions and causing tempers to flare as debate proceeds on the President's proposal to more than double the current annual spending on research, spending $30 billion on the research program over the next five years.

Both Republican and Democratic members of Congress expect the President's Strategic Defense Initiative, known popularly as ''Star Wars,'' to become controversial in Congress. How soon this will happen is open to question, but the fiery nature of what is to come was foreshadowed by an exchange during a hearing last year when Administration officials appeared on Capitol Hill to explain the fundamentals of ''Star Wars.''

Administration witnesses had acknowledged that a defensive system able to shoot down Soviet missiles in the so-called ''boost'' phase, soon after launching, would have to be triggered on extraordinarily short notice, so that the command decision might have to be made by computer.

''Perhaps we should run R2-D2 for President in the 1990's,'' Senator Paul E. Tsongas, Democrat of Massachusetts, retorted in anger, referring to the robot in the movie ''Star Wars.'' ''At least he'd be online all the time.''

''Has anyone told the President that he's out of the decision-making process?'' Mr. Tsongas demanded.

''I certainly haven't,'' replied the President's science adviser, George A. Keyworth II.

Robert S. Cooper, director of the Defense Advanced Research Projects Agency, chimed in that perhaps the President could carry a strategic defense trigger ''even into the bathroom.''

Senator Joseph R. Biden Jr., Democrat of Delaware, pressed hard for reassurance about whether the proposed defensive weapons might be fired by mistake, thus provoking the Soviet Union to launch a real attack. ''Let's assume that the President himself were to make a mistake,'' he said.

''Why?'' Dr. Cooper interrupted. ''We might have the technology so he couldn't make a mistake.''

''O.K.,'' Mr. Biden said. ''You've convinced me. You've convinced me that I don't want you running this program.''

Mr. Keyworth concluded with a key Administration argument: ''We see the investigation of strategic defense options as an absolutely vital catalyst to real arms control.''

Such sallies indicate the mood of many legislators, particularly Democrats, but they are only glancing blows at the research program itself. Indeed, no one has expressed a desire to cut back the program.

''There is an important underlying debate there but it's hard to see how the issue will get joined in a legislative context,'' said Representative Les Aspin, Democrat of Wisconsin, who is the new chairman of the House Armed Services Committee. ''As long as the program is only research, there is no legislative issue on which the opponents and proponents can line up on opposite sides. Even the most vociferous opponents say we ought to do research.''

The only issue this year, Mr. Aspin added, will be how much additional money to provide for research.

Yet the national debate over ''Star Wars'' goes on, as more and more fundamental questions are raised about it. The following are chief among them:

- Is this really only a research program, or a virtual commitment to deploy a defense should one become technically feasible?

- Is the President's goal of rendering nuclear weapons obsolete in fact a desirable objective, or do nuclear weapons play an essential role in preventing war between the superpowers?

- Is the goal realistically attainable?

- Is a lesser goal, say a partial defense that would protect American missiles and bombers but not the public, desirable in its own right, even though it would protect and enhance nuclear weapons, which is exactly counter to the President's stated goal of making such weapons obsolete?

- How would a future President manage the precarious business of actually deploying a defensive system?

- Are there any better alternatives?

The Program Takes Shape When, on March 23, 1983, Mr. Reagan unexpectedly called for intensified research to find a defense against ballistic missiles, he caught many of his subordinates flat-footed. Just hours before he spoke, the Pentagon official in charge of directed energy weapons, a major focus of the new defensive program, had told a Senate subcommittee that on technical grounds he could not recommend spending more money on the research.

Since then, Mr. Reagan's program has solidified and taken on a life of its own. The vast Federal bureaucracy of agencies, advisory committees, and consultants has begun to flesh out Mr. Reagan's generalized goal, often carrying it in directions that were not hinted at in the President's original formulation.

The Administration has stressed that the program is merely in a research stage and that any decision to actually build and deploy a defensive system will be made by future Presidents and Congresses.

Critics are skeptical that any program to which the President has committed himself so fully will wind up unfulfilled. ''If things work out at all, they're going to do it,'' predicts Spurgeon M. Keeny Jr., executive director of the private Arms Control Association.

The Defense Department has centralized its previously existing research programs into a single office, under Lieut. Gen. James A. Abrahamson. The level of actual spending in fiscal year 1985, the current year, is roughly comparable to what it would have been without the President's new emphasis, namely $1.4 billion. But now the program is poised for substantial expansion. The President has requested $3.7 billion for fiscal 1986. Additional money, roughly $300 million for fiscal year 1986, is in the budget of the Energy Department, which supports work at the national weapons laboratories.

What Congress will do to this budget in a year when it is looking for ways to reduce spending no one can say at this point. Key Republicans in the Senate are generally supportive of the President.

Senator Warner, chairman of the Senate subcommittee on strategic and theater nuclear forces, said in an interview that he favors giving the program roughly what the President has requested, although he added, ''I am not going to commit myself to the entire request.''

Senator Ted Stevens, Republican of Alaska, chairman of the Senate subcommittee for defense appropriations, called the Strategic Defense Initiative ''the highest priority I have.'' He said he might not endorse the full amount requested, but added that the program is at ''a critical juncture,'' at which it ''needs more money'' to determine whether breakthroughs are possible.

Key Democrats in the House are less supportive. Representative Aspin, the new head of the armed services committee, said it is ''likely that Congress will cut the money back some'' from what the Administration requested. Representative Joseph P. Addabbo, Democrat of Queens, chairman of the subcommittee on defense appropriations, said he hoped to hold the program at roughly its current level, with a small increase to cover inflation.

One possibility, which has been sketched out but not recommended by the Congressional Budget Office, would be to stretch the spending requested over six years instead of five.

Critics say they fear that the program will now steamroller, with support from an ever larger array of military contractors, lobbyists, technologists and Congressmen, to the point it cannot be stopped.

Still, there is at least one precedent demonstrating that reversal is possible. In the early 1970's, the nation actually started deploying an antimissile defense to protect American missiles, but then dismantled it as unworkable and expensive.

The most surprising unaddressed question in the emerging ''Star Wars'' debate is the validity of the goal itself. The President's long-range objective is, in a sense, breathtaking. It is nothing less than a defensive system that could intercept and destroy Soviet ballistic missiles in flight before they reached America's soil or the soil of American allies.

Such a system could eliminate the threat posed by nuclear weapons and make it possible to get rid of such weapons entirely through arms control agreements. The President has made it unequivocally clear what his ultimate goal is: ''To eliminate the weapons themselves.''

That strikes a resonant chord among many people who live in dread that some day the thousands of existing nuclear warheads will be fired. Even leading critics of the President's proposed system say that if they really thought it would work, they would be all for it.

Preserving the Peace

But not everyone agrees that a perfect defense against nuclear weapons, and their eventual elimination, would be desirable, at least not without much more thought about the consequences.

Some arms control experts say the fear of nuclear weapons has preserved the peace between the two superpowers for the last four decades. And, while these experts say they are eager to see the overwhelming size of world nuclear arsenals reduced to protect the world from complete destruction in a nuclear holocaust, they are reluctant to give up nuclear weapons entirely unless something they consider a better guarantor of the peace is at hand.

Lieut. Gen. Brent Scowcroft, retired, who headed a major study of strategic forces for the Reagan Administration, has said that the United States decided more than three decades ago to protect itself ''on the cheap'' with nuclear weapons instead of building up conventional forces. If strategic defenses deployed by both superpowers eventually nullify nuclear weapons, he said, American conventional forces will have to be beefed up, or the world will be ''safe for conventional Soviet aggression.''

Other experts suggest that if the Administration is serious about relying on defense it should go all the way and propose a large civil defense program, complete with evacuation plans and protective shelters and periodic drills. Such considerations have seldom been discussed.

The most thoroughly debated question is the one that can't be answered yet, the question that the Strategic Defense Initiative research program will explore: Is a defense that would protect the nation from ballistic missile attack both technologically and economically feasible?

Ten to fifteen years ago, the nation confronted that issue and concluded that the job could not be done. But since then, many experts agree, there have been great strides in the technologies needed to build such a system, and the answer is a little less clear.

The Administration has assembled an impressive array of technical experts who say that it is at least possible, if vigorous research is pursued for the next two decades, that an effective defense for the entire population may become feasible. A panel of 50 scientists and engineers, drawn mostly from the Government, industry and weapons laboratories, reviewed the emerging technologies over four and a half months and reported last April ''a sense of optimism'' that the technological challenges ''are great but not insurmountable.''

Since then, some individuals on the panel have expressed pessimism, but the panel chairman, James C. Fletcher, former head of the National Aeronautics and Space Administration, has reiterated that ''the technological promise is rich'' and that ''effective defenses may indeed be possible.''

After interviewing key figures in the debate, John Maddox, the editor of Nature, the British science journal, concluded that ''the most common complaints against S.D.I., that it cannot work, seem to outsiders to be belied by the numbers of intelligent people who are passionately persuaded otherwise.''

But an equally impressive array of experts is skeptical that a leak-proof defense is possible, particularly if a determined enemy is simultaneously trying to find ways to overcome it. A second team of outside experts assembled by the Reagan Administration, headed by Fred S. Hoffman, performed a study under the aegis of the the Institute for Defense Analyses. The study concluded that, while a defense effective enough to preclude nuclear attacks might result from the program, ''it is more likely that the results will be more modest'' - namely a system that could protect military targets but might not be able to prevent ''catastrophic damage'' to people.

In an all-out attack, the study said, even modest leakage of missiles through the defense shield would be ''sufficient to destroy a very large part of our urban structure and population.''

Other experts assembled by the Union of Concerned Scientists, the Congressional Office of Technology Assessment and the Stanford Center for International Security and Arms Control, among others, have judged that the likelihood of developing a near-perfect defense is exceedingly remote.

Experts on both sides agree that it will be an uphill battle to develop weapons that can shoot effectively at long distances, sensors and tracking devices that can find and follow thousands of missiles and warheads and distinguish them from tens of thousands of decoys, and prodigious computer capabilities to manage a battle for survival that would be over in minutes. Such capabilities are not in hand now and may never be in hand. The potential for success in this endeavor probably won't be known for decades.

Since the President announced his original goal of a full-scale defense that would protect the population and make nuclear weapons obsolete, his program has taken on a life of its own and moved toward lesser goals as well. In particular, many of the Administration's experts and study groups have stressed that, even if a leak-proof, full-scale defense system is eventually found to not be possible, a partial defense good enough to insure that American missiles and bombers will survive may become feasible and will certainly be achievable much sooner than a full- scale defense system is.

Thus the argument over Star Wars is splitting into two separate debates that are seldom carefully distinguished. One is the debate triggered by the President's original vision: whether the United States should move away from the threat of massive nuclear retaliation to deter attacks and rely instead on a new, highly effective defensive shield to prevent attacks on American soil.

The other is whether the United States should turn to a partial defense to protect its missiles and bombers, thus insuring that they could survive a surprise attack and unleash a devastating retaliatory attack on any aggressor.

The two kinds of defense have opposing objectives. Mr. Reagan's full-scale defense seeks to do away with nuclear weapons. A partial defense seeks to enhance their retaliatory power.

Supporters of the President's program see no conflict between the two goals. They say that the President has always said that, until an effective defense is ready, the nation will continue to rely on the threat of nuclear retaliation to deter attacks. A partial defense, they say, would be valuable for this purpose and as a way station on the road to an overall defense. But critics of the program say it makes little sense to spend vast amounts to protect nuclear weapons if the ultimate goal is to get rid of them.

Either way, the debate over a limited defense raises wholly different questions from those asked in the debate over a full-scale defense, according to many experts. If the goal is to protect missiles rather than people, then the wisdom of deploying a limited defense depends on the nature of the threat to American missiles and an evaluation of whether there are better ways, such as dispersal, or hardening, or mobility, to keep the missiles invulnerable.

One former Defense Secretary, Harold Brown, possibly the most technically sophisticated individual to hold that post, said in a recent paper that ''technology does not offer even a reasonable prospect of a population defense'' but acknowledged that, under certain circumstances, a defensive system might be needed to protect American missiles. He said, however, that the missiles are not now in danger and are not likely to be in danger for the rest of the century.

Other critics contend that a limited defense would be especially provocative to the Soviet Union because the system would clearly not be able to cope with a massive Soviet attack, but might be effective against a weak retaliatory blow by the Soviets after a large, pre-emptive American strike.

Hans A. Bethe, the Nobel Prize-winning physicist, and three colleagues warned last year in a magazine article: ''It is difficult to imagine a system more likely to induce catastrophe than one that requires critical decisions by the second, is itself untested and fragile, and yet is threatening to the other side's retaliatory capability.''

If the research program does come up with a full-scale defense that is technically and economically feasible, then it would require extraordinary cooperation between the Soviet Union and the United States to get it deployed without major incident, according to experts on both sides of the debate.

Unless both sides deploy comparable defenses simultaneously, most experts say, the side with no defense might become terrified and start shooting at the emerging defenses of the other before they can be deployed.

The President himself put his finger on this fundamental truth when he announced, in a statement that was later much ridiculed, that he would be willing to share with the Soviet Union any defensive technologies that are developed by his new program.

The White House has subsequently played down this offer, apparently realizing that the new defensive system, if it works, will embody the nation's most sophisticated computers, sensors and other high-technology items, items that could be used not just in a defensive system, but in a variety of offensive weapons as well.

Defense Secretary Caspar W. Weinberger said in December 1983 that unilateral Soviet development of an effective defense ''would be one of the most frightening prospects I could imagine.'' A White House document issued in January said that, if the Soviets deployed a nationwide defense against ballistic missiles, ''deterrence would collapse, and we would have no choices between surrender and suicide.''

If Mr. Reagan's new program should find that a highly capable defense is possible, the document said, ''we would envision parallel United States and Soviet deployments.''

Little thought has been given to the problem of orchestrating this transition. Paul H. Nitze, the Administration's top arms control adviser, said in a recent speech that the period of transition from offense to defense might take decades and ''could be tricky'' to manage.

The kind of cooperation required between the superpowers to deploy full- scale ground- and land-based defenses has never occurred in recent diplomatic history, in the view of both proponents and opponents of the proposed systems.

Some critics doubt that such cooperation is likely. Others suggest that if the superpowers decide to work that closely together they should simply agree to get rid of their nuclear arsenals and avoid the enormous expense of building defenses. Still others insist that, if defense is technologically possible, if cooperation could be worked out, then the world would, in the end, be better off.

The Prospects

The great appeal of the Strategic Defense Initiative is that it seeks a ''technical fix'' to the current set of nuclear problems, in which the world finds itself vulnerable to a catastrophic barrage of tens of thousands of nuclear warheads, any one of which can wipe out a city.

As the Administration sees it, the superpowers will never agree to eliminate nuclear arms unless they have defensive systems as a sort of insurance policy to protect themselves against any cheating. In a recent interview, Mr. Reagan likened his proposed defenses to a gas mask, always ready in case of need.

But critics are worried that any buildup of defensive systems would set off another arms race. The last attempt to deploy effective missile defenses, in the early 1970's, led to the development of the most feared offensive missiles in the current arsenals: the MIRV's or multiple independently targetable re-entry vehicles, designed to overwhelm defenses by releasing many warheads from a single missile.

These critics propose instead a political solution, namely more intense arms control negotiations.

However, years of arms control negotiations have produced only a steady, enormous buildup of nuclear arsenals.

As the two superpowers head into the arms control negotiations in Geneva next week, their positions on strategic defenses seem irreconcilable. Top Soviet officials are insisting that there can be no progress in limiting strategic and intermediate-range missiles at the talks, which is the prime American goal, unless there is also progress in limiting space and defensive weapons.

The American team, however, appears to have ruled out any concessions that would reduce the Star Wars research program or hinder later deployment of a defensive system. At a Senate hearing on Feb. 21, Fred C. Ikle, Under Secretary of Defense for policy, said, ''It is not our intention to negotiate limitations on strategic defenses,'' largely because ''we are engaged in a research program that could not be limited in any event.''

Senator Carl Levin, Democrat of Michigan, takes a different view. ''Star Wars is based on the fantasy that we can gain absolute security by developing new technology not vulnerable to countermeasures,'' he says.

At the hearing, Mr. Levin asked Mr. Ikle if he meant that ''research into space defense and deployment of space defense are not on the negotiating table in Geneva.''

Mr. Ikle responded, ''They are not things to be given up.'' He said the negotiators could discuss how to coordinate the deployment and phasing in of defensive systems, and the phasing down of offensive systems, but not negotiate about ''giving it up.'' The prospects of any prompt agreement, most observers agree, appear slim.

By Leslie H. Gelb

More than two and a half years after President Reagan broached the idea of a space-based defense, many Administration experts and critics alike remain uncertain about the consequences of such a defense for nuclear strategy and arms control. Yet almost all in the Government are going along with the program and, as a result, it has moved forward significantly in the past six months.

Indeed, the prevailing view now is that it will become harder and harder to turn back - even though Administration officials and legislators acknowledge that there is deep confusion about the purposes and consequences of ''Star Wars,'' as the proposed system is popularly known.

Despite the gathering momentum, key Administration officials say the program has not reached the point of no return. They say they are waiting for the opportunity to get the President to authorize measures that will take it even further before he leaves office in 1989, so his successor will be more or less compelled to forge ahead.

The first clear-cut result of the program seems to be that the world of the Antiballistic Missile Treaty of 1972, a world essentially without defenses against missile attack, will never be the same.

The conditions of that world, with the United States and the Soviet Union each limited to one missile defense site, are being eroded by the new technology and treaty loopholes. Both sides are exploiting treaty ambiguities, although each says it believes the other is more guilty of this.

The result is the development of antitactical ballistic missiles, antisatellite weapons and large radars. All of these improve antiballistic missile capabilities, the very thing the treaty was framed to severely limit.

The summit meeting between Mr. Reagan and Mikhail S. Gorbachev, the Soviet leader, made no progress in this respect. And, for all the apparent agreement at the top of the Reagan Administration, there are serious internal strains over how to proceed.

Several key officials acknowledge that Administration goals are still suspended somewhere between Mr. Reagan's dream of total defense of the American people from missile attack and the more proximate prospects for improving deterrence or protecting missile retaliatory forces.

Officials also acknowledge that a struggle is beginning over how to measure the ultimate cost-effectiveness of space-based defenses.

In particular, they point to a fight brewing between Defense Secretary Caspar W. Weinberger and his key aides on one side and Paul H. Nitze, the State Department's senior arms-control adviser, on the other. In recent Congressional testimony, Mr. Weinberger leveled a broadside against Mr. Nitze's insistence that defenses ultimately be judged in terms of their cost and effectiveness against offenses.

The President and most of his top aides are also trying to make certain that no future arms-control agreement will close off the Strategic Defense Initiative, the formal name for the ''Star Wars'' program.

Given Mr. Reagan's opposition to compromise on the Strategic Defense Initiative, officials who work for him engage in a kind of muted shadow-boxing. Most refuse to contemplate negotiating restraints on ''Star Wars'' with Moscow, some in the hope that this will kill off prospects for an arms control process that they believe harms American interests. Some State Department officials want to use ''Star Wars'' as a bargaining chip for cuts in Soviet offensive forces.

But it is clear from conversations in Washington and Moscow that neither these officials nor Soviet officials have figured out how to limit research and close treaty loopholes, if that were mutually desired. Those tasks are understood by most to be exceedingly complicated.

The parties within the Administration and Congress to these various disputes - over the goals of defending people or weapons, standards for judging prospects and arms control - have reached a kind of equilibrium. Neither side prevails. The result is that the established policy and the programs chug right along, more slowly than if there were unity, but forward nonetheless. And even some Soviet officials wonder aloud whether the march toward defenses can be stopped.

The single most compelling reason for this is the force of Mr. Reagan's commitment and vision of transforming nuclear strategy from deterrence based on the threat of retaliation to peace based on effective defense. Administration skeptics say they dare not question this vision. Legislators raise plenty of questions, but say they think it necessary for reasons of prudence and politics to approve funds to keep the initiative going.

There is also the cloudiness of the critics' position. The critics say they favor only research, and the Administration responds that it is doing only research. The critics say defenses are unaffordable, unworkable and bad, but that case is hard to make conclusively before more research is done.

And there is the allure of exotic technologies. So much that seemed impossible in the past is now a reality. Businesses and research institutions are being drawn into the space-research orbit by lucrative contracts. European allies who express alarm about arms control and the undermining of alliance strategy are tantalized by the research money and technology.

But there are also countervailing pressures. In particular, Congress and the Administration will be wrestling with increased efforts to cut military spending generally.

Nonetheless, the consensus is that a continuing and probably extensive research effort is virtually inevitable. This is particularly true as long as the Soviet Union also seems bent on some sort of space- or land-based missile defense, though the precise nature of what that is remains unclear.

Representative Les Aspin, Democrat of Wisconsin, chairman of the House Armed Services Committee, says the ''commitment to S.D.I. has grown substantially, even though its feasibility and good sense have been no better demonstrated today than they were when the President first spoke of the idea.''

''There's the feeling that there's no really big decision to make now because it's just a research program,'' he said. ''So all we're really doing is taking the proposed S.D.I. budget and trimming it back strictly on grounds that Mr. Reagan is asking for big increases each year and that it isn't wise to have such large increases at the initial stages of annnnnghy advanced technological program.

''Given all the factors, we have no real other choice than to do this, which means keeping the program going but at a slower pace.''

In the process, Mr. Aspin said, ''the real danger is that we will end up destroying the idea of deterrence without achieving the perfect world of defense.''

In March 1983, when Mr. Reagan began his program, he attacked the traditional theory of deterrence by retaliation as immoral and unreliable. His goal was grand, to make nuclear weapons ''impotent and obsolete.''

Several Administration officials now acknowledge that this went too far too fast. Even if Mr. Reagan's vision comes to pass, it might be 20 years or more away. In the meantime, the United States would have to rely on offensive forces and deterrence through retaliation. So, officials say, they began to tone down their public statements somewhat, to ''enhancing deterrence.'' Along the way, the goals were left in some confusion.

On May 30, according to the officials, Mr. Reagan issued National Security Decision Directive 172. It states bluntly, ''U.S. policy supports the basic principles that our existing method of deterrence and NATO's strategy of flexible response remain fully valid, and must be fully supported as long as there is no more effective alternative for preventing war.''

Based on this, the Administration published a special report in June. At one point, in accord with the directive, it proclaimed that ''successful S.D.I. research and development of defense options would not lead to abandonment of deterrence but rather to an enhancement of deterrence and an evolution in the weapons of deterrence through the contribution of defensive systems.''

But the original goal also found its way into the report: ''The purpose of the defensive options we seek is clear - to find a means to destroy attacking ballistic missiles before they can reach any of their potential targets.''

The emphasis, the report says, is on ''eliminating the general threat posed by ballistic missiles.''

The report added that the ''goal of our research is not, and cannot be, simply to protect our retaliatory forces from attack.'' What to Defend: Missiles or People?

Tucked away inside this larger debate is a more immediate question, namely whether initial ''Star Wars'' deployments should be used to defend missile silos and other military targets or whether they should defend people.

Administration officials are at pains to deny that they have any intent of turning Mr. Reagan's vision away from defending people toward defending weapons. Many of them say they feel this would knock the bottom out of public support for the effort. But some legislators, like Mr. Aspin and Senator Albert Gore Jr., Democrat of Tennessee, maintain that protecting military targets is the real goal.

Talking of the first stages of deployment, Fred C. Ikle, Under Secretary of Defense for Policy, said, ''The first impact of ballistic missile defense of the new technology rather than the traditional defense will be to make it more difficult for the aggressor to destroy all missile silos and command and control centers.''

The publicly expressed concerns and the logic of Administration policy have tended to go more in the direction of defending military targets from the beginning. When President Reagan spoke of ''the window of vulnerability'' in his first years in office, that is what he meant - that American missiles and command centers were vulnerable and needed to be defended. This problem has never been solved, although two years ago a Reagan commission on strategic forces said that the problem never existed in the first place.

Nevertheless, many top Administration officials call this their No. 1 strategic worry, and say missile defense is the only answer.

They reason that the best way to solve this problem is to get Moscow to get rid of its large land-based missiles, but the Russians will not go along.

A second possible solution is to deploy mobile missiles, which would be less vulnerable. But the Administration has proposed banning these because Moscow would have an advantage, being able to deploy them anywhere in the Soviet Union.

A third possible solution is greater reliance on submarine-launched missiles. But there is no telling how long submarines can remain invulnerable.

That leaves Washington, according to this reasoning, with its fourth and last option: defending its missile sites.

A senior Administration arms control adviser said in an interview that ''without S.D.I. we have real problems sustaining deterrence.''

Still, he went on to reject the fourth option, which is sometimes called hard-site or point or terminal defense, as impractical.

''Once you're into this, there is no way to keep the defenses limited to silo defense and prevent them from spreading to population defense,'' he said. ''We cannot inspect, verify and control such a restricted system, especially if it were to be space-based rather than ground-based.''

In the absence of further offensive agreements, this adviser and others argued that laying the basis for population defense could ultimately force each side into offensive buildups.

Like others, this official rejected outright the idea of limiting such a system to ground-based defenses. He said he thought Moscow, which has had more experience with these defenses, would have an unacceptable advantage. This official and others said Soviet officials have been quietly expressing interest in such a deal. Interviews with Soviet officials did not substantiate this. Buying the Most For the Money Even as the debate over protecting people or weapons continues, a new and equally portentous one is brewing over judging progress on research. Mr. Reagan's May directive says, ''Within the S.D.I. research program, we will judge defenses to be desirable only if they are survivable and cost-effective at the margin.''

Whether the system will be able to survive an attack is a question that will not be answered for some time. In the meantime, ''Star Wars'' progress was to be determined by whether research would show that it would be cheaper at the margin - that is, after all the basics are paid for - to add a unit of defense or an offensive warhead. The notion here is that if adding offenses would be less expensive, defenses would make no sense.

Mr. Nitze, the State Department's senior arms-control adviser, first used this criterion a year ago as a key test of the system's prospective cost-effectiveness.

But on Oct. 31 before the Senate Foreign Relations Committee, Defense Secretary Weinberger was asked about this idea. He responded: ''Well, I have to say, Senator, that I really do not know what cost-effective at the margins means. It is one of those nice phrases that rolls around easily off the tongue and people nod rather approvingly because it sounds rather profound.

''I have the greatest admiration for Ambassador Nitze, but I do not know specifically what he has in mind with that. If he means is it less expensive to build strategic defenses than continually to engage in trying to add offensive systems, I would say the syllogism proves itself. It is clearly less expensive because the defense can in effect ultimately, if it is as effective as we hope it is, make it quite apparent that further offensive systems are not useful.''

Mr. Weinberger added: ''I cannot conceive of strategic defense being more costly than the constant need to modernize and strengthen as each side makes a move to which the other side has to make a response.''

Asked if he would change his mind if a ''Star Wars'' system were found to be more costly, he said, ''No sir, I would not, because I would think the additional cost in protecting people's lives, in protecting this nation, would be far worth anything that it would cost.''

Richard N. Perle, Assistant Secretary of Defense for International Security Policy, sought to explain this further in an interview by saying that Mr. Weinberger ''just did not want cost-effectiveness to be the sole criterion, and that he wanted to make people see the difficulties in interpretation of cost-effectiveness.''

Mr. Gore said: ''Any decision to discard this criterion would strip the program and the concept of its last shred of intellectual legitimacy. It would only stimulate a race to deploy offensive countermeasures. This was the realization that led us to the ABM Treaty in the first place. If they do this, they're saying, 'Damn logic, damn reasoned debate, full speed ahead!' '' Strategy Switch: Offense to Defense As these problems are resolved, the Administration will also have to tackle the question that has given official planners the most trouble: namely, how to make the transition from a world dominated by offensive nuclear forces to one dominated by defenses.

For four decades, deterrence has rested on the idea that no matter which side struck first and no matter how vigorous the blow, the other could and would retaliate with a devastating blow. Thus, both would know there could be no meaningful victory, and neither would strike first.

The Administration contends that deterrence based on the threat of mutual annihilation is immoral. Further, it insists that technologies in the making will allow Moscow to make first strikes that could be successful.

The transition period, in which the Administration envisages a combination of offenses and defenses, could last 10, 20 or 30 years. And in the opinion of many, like Mr. Aspin, this period ''would be far more dangerous and unstable than anything we've lived through so far.''

The nightmare some imagine is that, for the first time, nuclear war might be made thinkable, and military planners would be able to calculate nuclear victory as follows: a first strike that knocks out more than 90 percent of the victim's offensive nuclear forces, plus defenses good enough to blunt most of what remained for a retaliatory blow.

Mr. Ikle and Mr. Perle say defenses will make nuclear war less thinkable, not more so. ''From the moment deployment of defenses begins,'' Mr. Perle said, ''you've complicated Soviet calculations needed for a first strike. Because of the defenses, Moscow could not count on being able to destroy enough of the retaliatory forces to make a first strike worthwhile.''

But from a wide range of military and civilian planners in the Administration it appears that, as one of them put it, ''We have not begun to think about, let alone explain to others, exactly what combinations of offenses and defenses would end up making the balance more or less stable.''

Besides, the general view among these experts is that the transition from offenses to defenses could not be made safely without Russian cooperation. Getting Moscow To Go Along The Administration's public position on getting Soviet cooperation is upbeat. Mr. Ikle said agreement ''won't come soon,'' but added, ''In the long term, it is far more plausible that the Soviets will agree with us on the new strategic order that eliminates mass destruction of the Soviet Union if nuclear war were to break out.''

To bring Moscow along, Mr. Reagan has offered to share ''Star Wars'' technology, although in private conversations, few in the Administration say this would be plausible.

Mr. Reagan has also ordered that all ''Star Wars'' programs be conducted in accordance with a ''strict interpretation'' of the Antiballistic Missile Treaty. Even critics of the program concede that this structure has been followed - with the arguable exception of one or two planned tests. The ''Star Wars'' testing program has been limited to subcomponents, as distinguished from antiballistic missile components or systems themselves.

This structure has been followed despite the Administration's assertion that the treaty actually allows development and testing of components and full systems of the new technologies.

Many arms experts dispute this interpretation, among them Gerard C. Smith, the chief negotiator of the treaty. But the matter remains moot as long as the White House continues to say it will not avail itself of the supposed legal rights.

In any event, Mr. Reagan tried to convince Mr. Gorbachev of the virtues of space-based defenses at their meeting in Geneva last month. By all accounts, he got nowhere. Moscow's position remains that it will agree to cuts in strategic nuclear forces only if Washington agrees to restrict ''Star Wars'' to laboratory research.

As far as Mr. Smith is concerned, these positions will continue to block a treaty. A sizable number of Administration officials agree with him. ''The alternatives are clear: arms control or a shot at developing defenses,'' Mr. Smith said. ''As long as the President sticks to his position, we will have no arms treaty.''

Even if Moscow were to show interest in negotiating a transition from offense to defense, it is far from clear that the Administration is in a position to lay out how to do so.

As Mr. Ikle said: ''It's hard to talk to the Soviets about something we ourselves haven't thought through completely. We could discuss the transition only in the broadest terms.''

The betting inside and outside the Administration is that Moscow's most likely response to ''Star Wars'' development will continue to be threats of more missile deployments. That view was bolstered inadvertently in a letter Mr. Weinberger sent to Mr. Reagan just before the summit meeting.

In it, Mr. Weinberger wrote that if Moscow were to deploy defenses, ''even a probable territorial defense,'' such a development ''would require us to increase the number of our offensive forces.'' This stands in direct contrast to the Administration's public position, a basic principle of its negotiating stance, that defenses should make it easier to reduce offensive forces. The Future Of Arms Control With the arms talks stalemated, one-sided decisions by both nations and the march of technology are moving to erode the old order of the Antiballistic Missile Treaty, the world in which the superpowers agreed to maintain peace through the threat of mutual annihilation rather than through defenses.

That was a major conclusion of a recent report by the Office of Technology Assessment, a research arm of the Congress. ''The inherent limitations of language and the rapid pace of technology,'' the report said, ''make it impossible to develop clear, unambiguous and objective standards by which to measure all possible research programs'' covered by the treaty.

One of many examples the report cites is one element of the space-based defense system called the ''airborne optical adjunct.'' The Pentagon plans to test this element to determine the feasibility of using optical sensors from an aircraft. Calling the element an adjunct or a subcomponent, the report says, ''depends less on objective determinations of capability than on how one defined those terms.''

The report also notes Moscow's deployment of a radar at Abalakovo, in Siberia. Administration officials say the installation is a ballistic-missile early warning radar and say it violates the treaty stipulation that such radars can be situated only on the peripheries of the two nations.

The treaty permits space-tracking radars to be placed anywhere, and does not define the two kinds of radars. Moscow insists the Abalakovo radar is for space tracking and is thus not a treaty violation. There is no disputing the fact that the deployment of such radars in numbers in both countries would clearly defeat the purpose of the treaty.

Also, because the treaty only limits defenses against strategic, or long-range, missiles, Moscow has moved sharply to develop ballistic missile systems for use against medium-range missiles, sometimes known as antitactical systems. The Administration is now talking about developing its own weapons against medium-range missiles.

The report also points to ''the great overlap'' between antisatellite technologies and antiballistic missile technologies. Moscow has a rudimentary antisatellite weapon, and Washington is testing a more advanced one. Moscow has proposed a ban and Washington has rejected the idea.

''The great loophole in the ABM Treaty,'' Mr. Smith said, ''is not whether it permits the development of new exotic technologies, but whether, under the guise of antisatellite weapons and antitactical ballistic missile systems and radars, antiballistic missile defenses will emerge anyway. As I understand, the Administration intends to do just this.''

Administration officials deny that this is their purpose, but acknowledge that they plan to move ahead in these areas. Moscow has already done so.

Amid all the complexities and counterarguments, one point is clear: in the absence of new agreements to close gray areas in old treaties and to ban or limit the development of new technologies, antiballistic missile capabilities will increase significantly on both sides in the coming decade.

A 'STAR WARS' UPDATE

On March 23, 1983, President Reagan called on American scientists to find ways to erect a missile defense shield in space to render nuclear weapons ''impotent and obsolete.''

In the months that followed, his proposal, formally called the Strategic Defense Initiative and popularly called ''Star Wars,'' began to be envisioned as one of the biggest research projects of all time, a five-year, $26 billion undertaking bigger than the Manhattan Project for the atomic bomb or the Apollo program to put men on the moon.

The space ''shield'' would not really be a shield but rather a complex network of systems, including laser beams, particle beams, electromagnetic ''sling-shot'' rail guns and sensing, tracking and aiming devices, all requiring extraordinary coordination at many different levels and stages. Many questions about the program arose.

Last March, The New York Times published a six-part series of articles exploring these questions. It reported, among other things, that a move toward a new era of strategic thinking and nuclear competition had begun; that the roots of the American effort went deep into past decades; that an experimental laser station already existed in California's mountains; that Soviet research, too, was forging ahead; that defensive space arms could also be used offensively with devastating effect, and that many answers still seemed elusive about the plan's ultimate wisdom and feasibility.

Since that time, there have been several key developments, including a summit meeting between the superpowers in Geneva at which ''Star Wars'' was a principal topic of discussion and dispute.

This three-part series follows those events and reports important new developments as the ''Star Wars'' plan and the national debate over it move ahead.

By William J. Broad

A deep rift has divided the leading scientists at work on President Reagan's antimissile defense plan.

Some of them charge that the program is being seriously threatened by exaggerated assertions, hyperbolic tests and costly public-relations razzle dazzle. Others vigorously deny that those working on the huge research project have any interest whatsoever in showmanship or hyperbole.

Critics outside the Government have long said the antimissile defense program, which is popularly known as ''Star Wars,'' is structured to promote the illusion of quick technical gains, no matter how great or small its actual accomplishments. But the new criticism is notable because it comes from prominent scientists who are at the forefront of the President's program. They say their technical credibility is at stake.

In the future, these Federal scientists say, showy tests may increasingly take precedence over cautious and technically sound science, especially as budget cuts force changes in the antimissile defense program, which is formally known as the Strategic Defense Initiative.

These scientists warn that the real danger is false public confidence in antimissile technology that might be wholly inadequate for the ambitious task of protecting the nation from the threat of enemy warheads.

In one case, dissident scientists have risked careers and jail sentences to publicize embarrassing top-secret details about widely touted programs, touching off both Federal hunts for those who disclosed the information and Congressional investigations of the charges.

''I'm very alarmed at the degree of hype, promises and a failure to focus on what this national program really is -a research program with lots of unanswered questions,'' said Dr. George H. Miller, head of defense programs at the Lawrence Livermore National Laboratory in Livermore, Calif. ''I'm afraid the public is losing sight of how difficult this job is.''

Dr. Roger L. Hagengruber, director of system studies at the Sandia National Laboratory in Albuquerque, N.M., asked, ''Will the science be negatively affected by the fact that there's so much pressure for stunts and demonstrations?''

''Clearly the answer is yes, especially as the dollars go down,'' he said. ''The need for progress in a program of this size is irreducible.''

Staunch defenders of the antimissile plan, including its director, deny that the program contains any hint of showmanship. But other key officials say it has long been structured with an eye to public relations.

''Salesmanship is clearly a factor,'' said Lieut. Col. Michael Havey, formerly a senior analyst on antimissile issues in the President's Office of Science and Technology Policy. ''It has to be when you're dealing with people. But what's important is that we're selling a quality product.''

He added, ''It's not been anything but honorable men trying to find the best way to convince the public at large, and Congress in particular, that we have a viable program, both technically and politically.''

From the start, program officials have acknowledged the need for stirring demonstrations. Dr. Gerold Yonas, the program's chief scientist, told a Georgetown University symposium in September 1984 that one of the plan's biggest challenges would be to build public and Congressional support, as well as gaining the support of America's allies. The task, he said, called for ''visible technology achievements.''

In private, ''Star Wars'' officials have often used acronyms that are evocative of salesmanship, especially in planning for highly visible technology tests. The initial name for these was Beacon, for Bold Experiments to Advance Confidence. Later, the name for such a project became STAR, for Significant Technical Achievements and Research.

Of the 1,000 or so contracts and projects in the ''Star Wars'' program, only about 10 have reportedly been selected for STAR roles. The criteria for their selection are whether a given project is making at least some scientific gains and whether it can be evocative of great technological strides.

''Early on there was a series of Beacons that was rejected as being too showy,'' said an official of a large aerospace firm, who added: ''There is history to show that stunts are helpful, distasteful though they may be in some ways.''

Examples of early Beacons are said to include the bouncing of a laser beam off the space shuttle in June, the demolition of a stationary missile during a laser test in New Mexico in September, and the destruction of a mock Soviet missile by a speeding projectile in November.

According to past and present Government officials, a STAR gets a lot of money and attention. In a rare public reference to this aspect of the program, Dr. Edward Teller, a key promoter of the antimissile plan and principal developer of the hydrogen bomb, told a London audience in June that major STAR projects were expected to cost between $500 million and $2 billion each, and that several were anticipated in the next two or three years.

The chief booster of such demonstrations is the director of the antimissile plan, Lieut. Gen. James A. Abrahamson of the Air Force, who has reiterated in speeches and Congressional testimony that breakthroughs are being made at an ''incredible pace.'' Scientists Level Blast of Criticism In October he told Congress that the New Mexico laser test ''demonstrated graphically the lethality of this technology.'' Also in October, he told the Philadelphia World Affairs Council that ''surprising progress'' had been made that meant the nation could deploy a workable space shield at least a decade sooner than expected.

Such assertions, however, have begun to irritate scientists at the forefront of the antimissile project, whose research has shown actual progress on putting into effect the President's vision of a space shield.

''There are some things we can do,'' said Dr. Miller of the Livermore laboratory, which employs 8,000 workers and scientists. ''We probably could build a strategic defense that would be 50 percent effective against the current Soviet threat, and that may be interesting. But we can't do what the President asked for. That's clearly in the research stage. And I'm afraid the public is getting the opinion that it's closer than it really is.''

In November, rebellious researchers leveled an unusual blast of public criticism at what they viewed as overselling. The criticism appeared in Defense Week, a respected industry publication. In a lead article headlined ''Expert Decries Harmful Hyperbole,'' Dr. Cornelius F. Coll 3d, director of ''Star Wars'' system studies at the Livermore laboratory, charged that overstatements by Pentagon officials were imperiling the program. Dr. Coll, the chief critic cited in the article, singled out estimates of the cost of an antimissile defense, saying they were unrealistically low.

''This job is difficult enough without having to defend hyperbole and exaggeration,'' he said.

''It's more important to this lab that our technical credibility be sustained than it is that 'Star Wars' becomes a reality,'' Dr. Coll added. ''There's going to be life after 'Star Wars.' ''

Federal laboratories, of which Livermore is one of the largest and most diverse, have long prided themselves on what they see as their objectivity. In contrast, they view contractors as beholden to Federal patrons, who control lucrative contract awards. Federal labs also see themselves as wielding much clout since they are the pioneers of many key antimissile technologies, including lasers, particle beams and kinetic-energy weapons. One Metaphor: Captive Chicken In interviews in California and New Mexico, high officials at several Federal laboratories echoed Dr. Coll's and Dr. Miller's complaints, saying the nation's technical credibility is being threatened by sales pitches.

''There's a real danger in this hype atmosphere for certain programs to overpromise,'' said Dr. Stephen D. Rockwood, director of ''Star Wars'' research at the Los Alamos National Laboratory in New Mexico, which employs 7,000 workers.

Dr. Hagengruber of the Sandia lab, which has 8,000 employees, said, ''The more expensive a program is, and the more it gets to something as fundamental as nuclear weapons, the more impressive the merchandising efforts become.''

Dr. Hagengruber said a serious threat was that the emphasis on salesmanship could increasingly imperil the objective design of experiments, especially those meant to test the destructive power of beam weapons. ''There's a desire to have very early demonstrations, to show lethality,'' he said, adding that such tests can be ''contrived.''

''If, for example, one was going to demonstrate the lethality of microwaves, one could put a digital watch in the horn of a microwave generator, blow the watch apart, and say microwaves kill watches,'' he said. ''For the lay public and Congress, that might be impressive.''

''But,'' he continued, ''it's actually far removed from reality, and interferes in a way with more thoughtful experiments. These demonstrations have the potential to be what we call strap-down chicken tests, where you strap the chicken down, blow it apart it with a shotgun, and say shotguns kill chickens. But that's quite different from trying to kill a chicken in a dense forest while it's running away from you.''

Although Dr. Hagengruber declined to cite any particular demonstration as an example of such experiments, critics outside the Government have said the destruction of a missile in New Mexico in September represented more showmanship than science.

The stationary motor casing in the desert was meant to mimic a Soviet missile in flight, according to Pentagon officials. Close-up films and photos of the exploding missile were widely distributed, and were shown repeatedly on television before the Geneva summit meeting.

The weapon behind that test is known as Miracl, for Mid-infrared Advanced Chemical Laser. It was built in the late 1970's by TRW Inc. for the Navy, and was originally meant to investigate defense of American ships from enemy planes and missiles. Congress killed that program. But the Miracl laser was later resurrected by the Pentagon for lethality tests, and in 1984 was assembled at the White Sands Missile Range in New Mexico, a top-secret, $300 million installation surrounded by barbed wire and armed guards.

Miracl is ''the free world's highest average-power laser,'' according to the Pentagon, although it looks more like a giant diesel engine than a futuristic weapon. Its beam is fixed and cannot be directed at moving targets. The laser's delicate mirrors, dozens in all, are fashioned so that heat is removed by the circulation of 9,000 gallons of cold water. About 370 people are needed to operate the laser site.

In the test in September, the second stage of a Titan missile was put about half a mile from the laser. The casing, which carried no fuel, exploded after being irradiated by the Miracl beam for ''several seconds,'' Pentagon officials said, declining to be more specific about the time.

''This advance gives us greater confidence in our ability to focus the laser beam into a small spot at long range,'' General Abrahamson told the Philadelphia World Affairs Council, hailing it as one of the program's ''world-class breakthroughs.''

Critics outside the Government, however, note that in space an antimissile laser would have to fire its beam thousands of miles. They add that for decades big lasers have been used to burn holes in metal over short ranges.

On another score, these critics say, the Miracl test was misleading. ''The impression was that the laser blew it apart,'' said John E. Pike, head of space policy for the Federation of American Scientists, a nonprofit group based in Washington that is generally skeptical of the antimissile plan. ''But it was the gadget at the top, the cross bar that was ostensibly there for dynamic loading, with the cables pulling down, that caused it to fly to pieces. The test looked much more impressive than it was.''

In November, a different test was publicized when General Abrahamson told a space technology conference in Colorado that the antimissile program had recently succeeding in destroying a one-third-sized mock-up of a Soviet SS-18 missile, perhaps the most threatening weapon in the Russian arsenal.

Displaying a photograph of the splintered booster, he said the test demonstrated the antimissile potential of the electromagnetic railgun, an experimental kinetic-energy weapon that could be based in space. The audience, made up of hundreds of Pentagon officials, military industry executives and reporters, broke into applause at the sight of the crumpled booster.

But after the presentation, in response to questions at a much smaller briefing, General Abrahamson revealed that the damage had not actually been done by an electromagnetic railgun but by a hardened projectile fired from an air gun, a technology much less futuristic. The modern air gun was developed in France in the early 18th century.

Dissidents in the Pentagon's antimissile program seldom publicly criticize Miracl tests, destruction of mock boosters, or other specific demonstrations. Instead their complaints are usually general and concentrate on policy trends. In one case, however, researchers became so upset by what they view as exaggeration and hyperbole that they broke the security laws.

The episode concerns development of the X-ray laser. This device, powered by a nuclear bomb, is meant to fire powerful beams of radiation across space to destroy enemy missiles.

In April, Dr. Teller alluded to new X-ray laser breakthroughs in a speech at the University of California. Some time later, according to press reports, he took the news to the White House. President Reagan later directed that an extra $100 million be channeled into the nation's X-ray laser effort.

But anonymous rebels soon objected to the purported advances, risking jail sentences to give journalists top-secret details of failed nuclear X-ray laser tests. In its Nov. 8 issue, Science magazine, a widely respected scientific journal, reported that a key X-ray focusing element had proved defective, and had failed in an experiment at the Nevada nuclear weapons test site.

In addition, the journal said, a key monitoring device had been miscalibrated, rendering the results of earlier tests uncertain. Further disclosures to the press revealed that the Government intended to forge ahead with its next X-ray laser test, even though the design flaw had not been eliminated.

On Dec. 6, 30 members of Congress sent a letter to Defense Secretary Caspar W. Weinberger urging him to postpone the test, which was to cost $30 million, until the problems could be fixed. They also asked for an ''immediate'' briefing on the X-ray laser program, including the experimental flaw.

Federal officials have publicly confirmed that there are unresolved technical problems in the X-ray laser experiments, but they have characterized them as minor.

With the X-ray laser and antimissile tests in general, dissident scientists contend that serious research is threatened with distortion by the rush to impress the President, Congress and the American public with antimissile feats. It is a charge that General Abrahamson, the program director, vigorously denies. He says the Pentagon has no interest whatsoever in showmanship, but much concern about keeping American citizens well informed.

''We're trying to run an open program,'' he said in an interview. ''Within the limits of security considerations, we owe the nation procedures that allow people to see what we're doing, the real rate of progress, so they can make their own judgments.''

He laid criticism within the ranks of antimissile scientists to malcontents who were jealous of the technical advances and well-funded projects of their rivals. ''In every organization there are people who are more optimistic and more pessimistic,'' he added. ''Since we don't impose strict censorship, I'm sure there are some who think parts of the program won't pay off in the way some other people have described them.''

Dr. Yonas, the program's chief scientist, said he had fought a losing battle to keep Government officials from using such acronyms as Beacon and STAR, saying they falsely implied a concern with showmanship. He said the antimissile program did have a special category of ''significant experiments to resolve key technical issues,'' but he vigorously denied that any tests had been staged or their results exaggerated.

''The Miracl experiments were worthwhile and provided important information,'' he said. ''I don't consider doing experiments like that showmanship.''

Despite such denials, Federal scientists say showy demonstrations are normal in any area of science that requires a lot of public money. ''Blame the whole American approach to big science,'' said Dr. Rockwood, of the Los Alamos lab. ''Congress needs to see something. They aren't knowledgeable enough to judge inventions without some sort of demonstrations.''

In the antimissile program, Dr. Rockwood said, real experiments that resulted in breakthroughs would probably be kept secret, especially if they held promise for the penetration of an enemy's antimissile shield.

As for showy public-relations stunts, he said their potential for seriously distorting the nation's antimissile agenda could be minimized if key scientists and managers adhered to its deeper goals. ''If the programs are managed in that way,'' he said, ''then this overselling will not lead to vast waste.''

Merchandising pressure may increase because of cuts in the ''Star Wars'' budget, according to some dissident scientists. For fiscal 1986, Congress cut roughly a billion dollars from the Reagan Administration's request of $3.7 billion. Larger cuts loom, some Congressional sources say, estimating that the five-year antimissile research program may get little more than half the $26 billion originally sought.

The problem, as some dissident scientists see it, is that visible ''progress'' must be made no matter how much money is cut. Otherwise, the programs' sheer size makes them even more vulnerable. ''It happens everywhere, not just S.D.I.,'' said Dr. Hagengruber of the Sandia lab.

Whether real science or stunts, or a politic combination of the two, several future STAR projects are expected to revolve around laser tests on the space shuttle, according to scientists in Government and industry. These are to demonstrate the ability to find and track moving targets, in rehearsal for pointing a weapon.

Originally such tests had been grouped together under a Pentagon program titled Talon Gold, which was to have had a single space-based test aboard the space shuttle in 1988. But Pentagon officials killed that program and created a new one in which a series of pointing tests on the shuttle are scheduled for 1986, 1987 and 1988.

''You don't want to tie things together in an end-to-end system,'' said Colonel Havey, formerly with the White House. ''Too many things can go wrong. You need to demonstrate the components.''

At the Pentagon's request, these shuttle tests are to be publicized, according to officials of the National Aeronautics and Space Administration. Such openness is a break with official Defense Department policy, which calls for military shuttle missions and experiments to be classified as secret.

Paradoxically, the new openness means that routine launches of military communications satellites will be shrouded in secrecy but tests of advanced weapons will be displayed in public. Starting in 1986, there are to be two major shuttle-based experiments for the antimissile program each year, according to NASA officials.

During one shuttle mission, laser beams fired through a window of the European-built Spacelab are to strike one or more large mirrors mounted in the shuttle's payload bay, and then be reflected toward satellites or other targets, according to the magazine Aviation Week and Space Technology.

''Aside from its technical objectives,'' the magazine said, quoting authoritative Pentagon sources, ''the mission is designed to show that the S.D.I. project can produce significant results while building momentum to justify long-term continuation of the multibillion-dollar research effort.''

Despite fears of exaggeration, the dissidents in the antimissile program say real gains are being made, especially with neutral-particle beams and free-electron lasers, technical areas that have received little publicity so far. They add that these projects have become STAR programs and will be given more money and demonstrations. When such tests might occur is not yet publicly known.

Scientists in Government and industry, however, say there is a general push to advertise the fruits of the antimissile research before the 1988 Presidential election. Top Federal officials deny this charge. But in May, President Reagan's science adviser, Dr. George A. Keyworth 2d, told a meeting of military contractors that ''unequivocal proof'' of the feasibility of antimissile defense could be demonstrated by 1988 if the research was ''properly streamlined.''

After the speech, Dr. Keyworth was asked if he was speaking of demonstrations of missile interception in space. ''No,'' he answered, calling such tests a gimmick. ''If you put a big laser on a mountaintop and destroy a steel sphere a meter in diameter on another mountaintop a couple of hundred miles away, you've demonstrated technological feasibility a heck of a lot better than with space simulation.''

Dr. Keyworth, one of the most ardent supporters of the antimissile plan in the Reagan Administration, recently announced that he will resign his post at the end of the year. He has said he is completely satisfied with the direction of the President's program.

In the next few years increasingly showy laser demonstrations will probably be performed in the New Mexico desert, according to scientists in Government and industry. The Miracl laser, they say, is being equipped with a large beam director that will allow it to fire at moving targets, like large missiles.

Whether such exhibitions as pointing lasers out of the space shuttle and destroying missiles in the New Mexican desert will constitute ''unequivocal proof'' of the feasibility of the ''Star Wars'' defense, as Dr. Keyworth put it, is an issue that undoubtedly will be debated not only by Congress and the American public but also by the leading scientists at work on the antimissile program. With an eye to technical credibility, they say they are already worried by growing pressures to distort science for the sake of public relations.

Asked what the American public should expect from the antimissile program in the next two or three years, Dr. Hagengruber of Sandia replied: ''I expect they will not see the leaps and bounds in the technology they would all like to see. Their patience will wear thin, and that will be an added stimulus to stunts and demonstrations.''

He added: ''I think it's unfortunate. I would say it's very unfortunate because the progress that's being made and the work that's being done is valuable. But I think the environment is going to become much more stressful - what with the deficit, the political environment, the upcoming elections.''