NASA yesterday released new film footage showing that one of the space shuttle Challenger's solid-fuel boosters was defective and had begun spewing "an unusual plume," which appeared to be a flame, about 14 seconds before the explosion that destroyed the shuttle.

The film, the first significant break in the investigation of Tuesday's disaster that killed seven crew members, revealed that as of 59.82 seconds after liftoff, the booster on Challenger's right side had ruptured about one-third of the way up from its base and was emitting a plume of hot gases that appeared to grow larger until the explosion.

The film -- enhanced by computer and transferred to videotape -- was made by a 70mm camera located north of the launch pad that had a different view of the shuttle from that of the cameras that supplied the previously broadcast images.

Those cameras, situated south of the pad, could not see the right-hand booster and showed nothing amiss until about one second before the blast.

The solid rocket boosters, now even more critical as evidence in the investigation of the crash, were blown up on radio command from earth about 30 seconds after the explosion because of fears they might veer into an inhabited area.

NASA spokesman Hugh Harris declined to speculate on the significance of the plume, even refraining from calling it a flame. Harris said NASA's interim investigating board had not reached any conclusion as to whether the plume was a cause or an effect of the problems that befell Challenger. Harris said the National Aeronautics and Space Administration "cautions against drawing any conclusions from the pictures."

If the plume is confirmed after further investigation to be a jet of hot gases leaking from the solid rocket, it could have caused the explosion by heating the adjacent tank of liquid hydrogen fuel, almost like a blowtorch, and melting a hole that released the highly explosive hydrogen.

The film, as well as new still photographs also released last night, were the first bits of solid information given out by NASA since the space agency's massive investigation got under way Tuesday after the accident. They were released about 8:50 p.m. at a NASA briefing at the Kennedy Space Center in Florida. NASA officials declined to interpret or comment further on the film or its meaning. They said they released the materials because they were something new that could be shared with the public.

Earlier in the day acting NASA Administrator William R. Graham briefed members of Congress, showing them what was believed to be a different film that revealed the same plume.

The announcement followed a day of confusion in which NASA officials denied a variety of news reports that new clues had been found to implicate the solid rocket boosters.

In the immediate aftermath of the disaster, many aerospace scientists said they doubted the boosters were at fault because they continued flying out of the fireball.

The boosters were flying so well that Air Force technicians blew them up out of fear they would curve back toward populated areas. That act, it is now evident, may have destroyed physical evidence of what went wrong.

NASA officials, who have put up a virtual wall of silence since Tuesday's explosion, said yesterday that on Monday they would begin daily briefings on the progress of the official investigation. But one spokesman warned that the agency is not likely to reach a conclusion soon about the cause of the disaster. "We don't want the quick answer, we want the right answer," Harris said.

NASA spokesmen declined to confirm or deny a report in The New York Times that one of the boosters had suffered a sudden drop in propulsive power about 10 seconds before the blast. The report also said that when the booster lost power, the shuttle's five engines -- the three liquid-fueled engines at the back of the orbiter and each of the two solid-fuel engines -- immediately swiveled their nozzles to one side to keep the space ship flying straight. The Times also said that the three liquid-fueled engines then shut down before the blast.

One NASA spokesman at the Johnson Space Center in Houston said, "None of these things happened. The three main engines were burning right up to the time of the explosion."

Another NASA spokesman, Jim Mizell at the Kennedy Space Center in Cape Canaveral, gave a slightly different response. While conceding that the Times report "is a good engineering hypothesis, I would not go along with their conclusions at this time."

Meanwhile, in Florida, a NASA spokesman said the sea search for parts of the Challenger had been expanded to a 20,000-square-mile area ranging 90 miles out to sea and as far north as Savannah, Ga., near the point where a cone-like fragment has been recovered.

The massive effort now involves at least seven ships, 14 aircraft, underwater robots equipped with cameras, and Navy planes equipped with special "air-eye" devices, and has retrieved surprisingly large pieces.

Amid it all, at 11:39 a.m. yesterday, the time of the Tuesday explosion, a wreath was dropped into the sea from a helicopter in honor of the Challenger crew. The wreath was made up of white chrysanthemums and seven red carnations -- one for each of the dead astronauts.

Back on land, at Kennedy Space Center, about 5,000 NASA employes, many weeping, participated in a memorial service for the astronauts.

If the new scenario of what happened is correct, it suggests that there was a major defect in the solid-fuel booster that allowed its fuel to burn so unevenly that its heat melted through the side of the booster and allowed hot rocket exhaust gases to reach the hydrogen tank.

A congressional source who saw new footage said the "burn-through" appeared to be near the base of the solid booster, at about the level at which the shuttle orbiter is fastened to the hydrogen tank by metal struts.

This is also where liquid hydrogen and liquid oxygen are piped across from the tank to the main engines in the orbiter.

If the burn-through occurred at this spot, it would be near a joint between two of the four hollow cylindrical blocks of solid fuel that are stacked inside the booster's steel casing.

This, according to experts in solid fuel technology, could indicate that there were defects in the manufacture of the fuel that allowed it to burn faster near the joint than elsewhere.

When a solid fuel rocket burns normally, combustion takes place over the length of the inner surface of the stacked hollow cylinders. As the rocket flies, the burning is supposed to consume the fuel evenly, gradually working its way toward the outer casing. By the time the fires reach the casing's inner surface, however, all the fuel is supposed to be consumed and the rocket stops firing.

In a normal shuttle launch, the spent casings are jettisoned after two minutes of flight and automatically parachuted into the ocean for recovery and refueling. The casing is designed to withstand 20 uses.

If there was a defect in the way the fuel was manufactured, experts say, it could burn faster in some places and eat its way to the wall while there is still a raging inferno inside. Heat and flame could then melt a hole in the casing and spray out.

A similar kind of premature burnout occurred in smaller solid fuel rockets that were used on an earlier shuttle flight to boost communications satellites into a higher orbit after being released from the shuttle's cargo bay, according to NASA sources. In that flight, both boosters burned out too soon, leaving the satellites stranded in a uselessly low orbit.

One source close to the space program told The Post that if the solid rocket boosters are determined to have been a likely cause, NASA would probably try to replicate the accident by firing similar boosters on the ground while strapped, as on the shuttle at launch, to a large tank of liquid hydrogen.

On another front of the investigation, the search at sea, a Navy ship reportedly retrieved a 13-foot diameter cone from the sea 100 miles off of Savannah. It is possibly the top of the Challenger's fuel tank.

It was among the more than 3 tons of debris retrieved since the search effort got under way shortly after Tuesday's explosion.

According to the Associated Press, NASA also said it has found the nose of one of the boosters, complete with parachute and four motors designed to separate the boosters from the space shuttle when necessary. The discovery confirms that Challenger's astronauts had no warning of what was happening, or at least, not enough warning to have hit a "ditch button" that fires the booster separation motors.

As part of the search yesterday, underwater robots -- named "Sprint" and "Scorpio" -- surveyed the waters of the Atlantic off the Florida coast attempting to determine whether a large object detected by sonar on the ocean floor Friday could be part of the Challenger's crew cabin.

The object was detected in about 140 feet of water 30 miles east of Daytona Beach.

At the Kennedy Space Center, employes gathered under gray skies to pay tribute to the seven Challenger shuttle crew members killed in Tuesday's the launch disaster.

Drawing together on at the same viewing stands from which hundreds of spectators watched in horror when the shuttle blew up, the employes and their families grieved openly as prayers were offered.

An astronaut read the moving poem, "High Flight," in memorial tribute to the crew.

During the half-hour memorial service, Kennedy Space Center Director Richard G. Smith told the throng:

"While we mourn their passing, we must not lose sight of their beliefs, the desires of the families and loved ones, the pledge of President Reagan that we will push on . . . to fly the space shuttle again and establish a space station."

Veteran rocket engineers, spacecraft managers, and hardware technicians wept as "Taps" was played.