The state's worst ground fire in decades -- a vast arc of windblown flames that boiled in 40-foot walls, scorched miles of pine woods and burned a dozen homes and other property -- raged for a second day in Suffolk County yesterday. But last night its threat to a South Shore resort community appeared to ease, and officials said it might be brought under control today.

The fire, which posed Herculean hardships for weary firefighters, also raised a testy political issue between state authorities who anticipated airborne tankers to fight the flames and Federal officials who failed to fulfill a promise to deliver them yesterday. And police investigators raised another specter, saying that an arsonist may have been behind the blaze.

The fire remained out of control, with new flareups on the perimeter of the 12-square-mile blaze. But there were no reports of deaths or major injuries, no more homes or businesses were lost, and after a day of ground and air attacks on the flames, the huge clouds of smoke billowing on the horizon began to diminish and officials began to express hope that, with luck, the worst might be over.

"Everything looks much, much better," Gov. George E. Pataki said shortly after 6 P.M. as he returned to a command post from a helicopter flight over a 7,000-acre moonscape of scorched earth ringed by darkening fires. "What a difference a day makes. I'm now convinced that we will be getting the fire under control. The winds have died down and that's a great help."

Senator Alfonse M. D'Amato called the situation "a dramatic change from yesterday." He had accompanied the Governor throughout a day of high drama on the edge of a conflagration roaring through woodlands as dry as a tinderbox, whipped by winds that peaked at 25 miles an hour and gradually diminished.

Col. Ed Jacobi, Superintendent of the New York State Forest Rangers, agreed that the situation had improved dramatically. There were still brush and woods in the fire's path and the flames were not yet contained, he said, but added that firefighters planned an all-out assault beginning early this morning in the hope that the fire would be brought under control today.

By 1 A.M. today, the winds had ebbed to a near calm and a cool damp air had settled in over the Pine Barrens, aiding firefighters who continued to work through the night, clearing fire breaks and raking and dousing embers.

Even as the dangers faded, an inquiry into the fire's cause intensified. Detective Sgt. Robert Flood of the Suffolk County police said the authorities were investigating the possibility of arson and had recovered "physical evidence" near the place where the fire broke out on Thursday afternoon: pine woods south of the eastern campus of Suffolk County Community College in Westhampton.

Investigators, he said, had found evidence of three fires in the area about the same time. A fire earlier in the week that destroyed 3,500 acres of Pine Barrens at Rocky Point, 20 miles to the northwest, was also under investigation as suspicious.

Yesterday was a day of perils and measurable success for 2,000 volunteers from 174 fire companies across Long Island. With paramilitary tactics and, often, the unsung heroics of an epic battlefield, they plowed firebreaks, raced to flareups to save endangered houses in Westhampton and held a critical line at Montauk Highway to protect businesses and homes in Westhampton Beach.

To firefighters, it was a day to remember: walls of orange flame as tall as a four-story building bearing down on them, roaring winds of a kind that really big fires generate on their own, dark smoke that blotted out the world and made it impossible to breathe, a fire of awesome magnitude and power.

Mike Hoda, a volunteer firefighter in nearby Speonk and a man not used to confessing fear, recalled the inferno he had confronted. "I've been to some brush fires," he said, his soot-streaked face dripping with sweat. "This is the only one that really scared me, the unbelievable strength of it."

But it was also a day of confusion for political leaders and bureaucrats behind the lines. The trouble began when it became apparent that four C-130 airborne tankers that had been promised by President Clinton and officials of the Federal Emergency Management Agency were not coming from Minnesota.

The tankers had been mentioned all day by the Governor, Senator D'Amato and other state and local officials at the scene as the big weapons they could count on to break the grip of the devastating fire. Each tanker is capable of dropping up to 5,000 gallons of water on the fire.

But as the hours passed, and the airborne fighting was limited to six helicopters chopping through billowing smoke from a nearby lake to attack the blaze with 200-gallon water bombs, the Federal promises of big tankers remained unfilled.

The Governor said he called President Clinton about 1 A.M. and received pledges of total cooperation. But at 2 P.M., he said, he learned that the planes were not coming. Mr. Pataki's disappointment was open, almost palpable, and it appeared for a time that the spirit of common cause that usually crosses political lines in a disaster had been tarnished.

Later, James Lyons, the Under Secretary of Agriculture, who was sent by the President, said there had been a bureaucratic mix-up. "Due to mistakes in process, they didn't get here on time," he said. "We don't know exactly what the mistake was."

Then, the Governor was told that two tankers -- not four -- were on the way after all, and would arrive overnight, in time to be put in the air against the fire today. But by then, firefighters had made progress by dropping water from helicopters, and Mr. Pataki and Senator D'Amato were more upbeat and seemed less anxious to cross swords with the President and Federal bureaucrats.

"Everybody wants me to point the finger at the Federal Government," Mr. Pataki said. "I'm not. We hoped they would be here. They are not."

Senator D'Amato also refused to be drawn into criticism. "There was a goof-up," he said. "They're big enough to admit it. This is not a time to nit-pick."

The fire, after breaking out on Thursday, had leaped highways and railroad tracks, threatened the Suffolk County Airport and forced 600 residents of Westhampton, Westhampton Beach and Speonk to evacuate homes and businesses. Streets were jammed at times with people fleeing with clothes, pets and other possessions.

And while firefighters had notable successes protecting scores of homes and other property, the flames burned 12 houses and a lumberyard and other businesses, and scorched the brick Westhampton station of the Long Island Rail Road. Traffic on the railroad and on the area's highways was disrupted. Yesterday, as firefighters waged a ground war on the perimeter with hoses, shovels and picks, and helicopters with 200-gallon buckets ferried water from nearby Wildwood Lake, the worst fears -- that the flames would invade the more heavily populated areas of Westhampton Beach -- were not realized.

Hospitals in the area reported treating 46 people, nearly all of them firefighters who had suffered smoke inhalation.

Many of the 600 people who had been evacuated to high schools in Eastport and Hampton Bays returned to their homes yesterday -- a few eluding police blockades to reach homes on Depot Street or Station Road, near the Westhampton rail station, that had been destroyed or gutted by the flames. Most found homes intact.

There were a thousand worries, though. At one point, officials expressed concern that helicopters crisscrossing the area through the smoke might be in danger of midair collisions.

The Suffolk County Executive, Robert J. Gaffney, urged residents throughout the area to minimize the use of cellular phones and water to avoid interfering with the firefighters' efforts. He said the fire had burned an area six miles long and two miles wide, bounded roughly by Montauk Highway on the south, the Suffolk County Airport on the east, Speonk on the west and the Sunrise Highway and other roads on the north.

Long Island Rail Road service was shut down east of Shirley and was expected to remain closed through the weekend, according to a spokesman, Jim Dolan. Many local roads, including part of the Sunrise Highway, also remained closed.

Mr. Gaffney urged people heading for the Hamptons this weekend not to cancel their plans because of the fire. He said there were no problems east of Westhampton, and noted that drivers could use the Long Island Expressway to Riverhead and then head for either fork on the island.

A tour of parts of the burned area yesterday revealed a strange landscape where green woods had become charred pines standing like blackened sticks. Flames continued to lick at underbrush. Here and there, firefighters made their way through the stricken, eerily smoking realms.

At one point, Governor Pataki watched a group of firefighters hose down a house and beat back approaching flames. As the fire turned away, they began to whoop joyously, and the Governor waded into the smoking woods to pound the volunteers on the back.

"Great, great job!" he shouted.

Later, at a news briefing, he said: "It's one thing to see it from the sky. It's another thing to see the incredible bravery of the volunteer firefighters out there, risking their lives to protect us."