A Suffolk County police officer stops traffic at a checkpoint in East Moriches to keep sightseers away from the Coast Guard station. (Newsday / Audrey C. Tiernan)

At Kennedy Airport's International Terminal, longtime employees who are usually greeted with a wave and a nod weren't admitted yesterday unless they showed their identification cards.

At the Port Authority headquarters at the airport, a warning was repeatedly broadcast over the public address system that workers whose ID cards had expired would not be granted access.

And at the airport hotel, security guards carefully checked room passes before allowing anyone to enter.

All were visible signs of the stepped-up security at JFK following the crash of TWA Flight 800 - even though the disaster's cause is officially undetermined.

Officials were reluctant to reveal any other, less obvious safety measures. John Kampfe, spokesman for the Port Authority of New York, which manages JFK, LaGuardia and Newark airports, said, "We're pretty much doing the same thing that everybody else is doing from the president on down -- we're not talking about security. If we did, there would be no security.''

Airline officials said that they had been operating under tight security even before the crash.

Paul Turk, a spokesman for USAir, said, "The entire air travel system has been on an enhanced footing for months now. We are complying with FAA requirements, and if those change we will comply.''

Marta Laughlin, a spokeswoman for Northwest Airlines, said her company has "been in an increased level of safety at all of the airport terminals, including JFK, since last year, with multiple forms of identification checks and baggage questions.''

American Airlines acknowledged it had toughened security measures at Kennedy but declined to talk specifics. Kimberly King of Delta Airlines said, "The only thing we can confirm is that our security procedures at JFK exceed all federal requirements.''

Outside the International Terminal, security guard Pierre Louis Yves was stopping everybody attempting to enter the building and asking to see their tickets.

"I'm just doing my job," Yves said.

Inside, Ronald Armogan said he didn't believe anyone could stop a determined bomber - but showed a healthy respect for the efficiency of the security system at Kennedy.

On a previous flight, he said, security people had opened a bag of his because, with an X-ray machine, they had spotted a battery inside a toy in his luggage. "I brought a lot of toys this time, but I made sure I removed all the batteries because of what I experienced before,'' Armogan said.

Dexter Chambers contributed to this report.