The Federal Aviation Administration, as a result of lessons learned from a fiery desert test crash Dec. 1, is preparing regulations to improve impact protection provided by airline seats, FAA Administrator Donald D. Engen told a House Science and Technology subcommittee yesterday.

That crash of a remote-controlled jetliner loaded with instrumentation and dummies but no passengers was a joint effort by the FAA and the National Aeronautics and Space Administration.

The experiment is widely remembered for the giant fireball that appeared immediately after impact. Safety specialists had thought they could prevent it by using a special fuel additive called AMK (antimisting kerosene).

Engen conceded yesterday that the enormous, plane-engulfing fire was "a surprise." He said, "I am proceeding with all of our anticipated rule-making actions, except that with respect to AMK. We will wait for the complete analysis of data before deciding on further action in this area."

Airline seats have long been known as a problem in crashes. In some survivable crashes, seats have torn loose from the cabin floor, banging passengers into each other.

In the most recent major U.S. accident -- the Galaxy Airlines charter crash that killed 70 persons in Reno, Nev., Jan. 21 -- the only survivor was thrown free and landed on a highway, strapped in his seat.

"If you strengthen the seats, you have to strengthen the floor to which they are attached," Engen said. "So you have to do it in a way that can be engineered in."

Engen said he expects that the rule will be applied for seating on new aircraft built after a certain date and that refitting the existing fleet will not be necessary.

Engen also said that passengers could have survived the impact forces of the test crash and that FAA officials think that there was time, perhaps 20 seconds after impact, for some passengers to have escaped from the plane.

Some of the plane's seats bore "fire-blocking" fabric, and cameras that survived the accident showed that the seats equipped with it burned much more slowly than others, Engen said.

Rep. William Carney (R-N.Y.), who witnessed the crash, praised it as a worthwhile experiment, but told Engen yesterday, "I'm a layman, but there is no way that was a survivable accident. I don't care how much data you crush, no way."

Engen said, "In those 20 seconds or so . . . ."

Carney interrupted, saying, "One and one-half hours later, it was still burning."

Subcommittee members were shown films of the crash taken inside and outside the four-engine Boeing 720. The left wing struck the ground first but remained with the aircraft, and the wing's fuel tanks never ruptured.

The right wing, however, struck one of the metal "can openers" mounted on concrete on the desert floor to ensure that wing tanks would be ripped open, creating an ignition source for a fire.

The inboard right-wing engine and the fuselage were slashed open, cutting off the right wing and severely damaging a major structural beam. The engine provided a continuous source of heat as fuel poured out of the wings.

Dummies in the aircraft were restrained by their seat belts, and those placed in the forward brace position recommended in crash landings appeared to show little movement during impact.