Three survivors of the Air Florida crash here Jan. 13 testified yesterday that they knew something was frighteningly wrong even as the Boeing 737 accelerated down the runway at National Airport.

The fear turned to terror, they said, when the jet, shuddering violently from the moment after lift-off, struck the 14th Street bridge and left them groping for their lives in the icy Potomac River.

The plane was not "gaining the speed that I was used to" and after lift-off "felt like it was going to shake to pieces," passenger Bert Hamilton of Gaithersburg told the opening session of public federal hearings into the crash, which killed 78 people.

As the plane sank, Hamilton fumbled his way free of his seat belt and made it to a piece of wreckage. Passersby on the bridge shouted encouragement to him and other survivors, who tore open a life jacket bag with their teeth, screamed for a boat and found their hands too numb to grab hold of a lifeline dropped by a helicopter.

"The propellers were blowing the ice around," survivor Patricia Felch testified. "It really hurt." Flight attendant Kelly Duncan panicked and shouted, "We're going to die out here," according to Felch, who was close to her in the water.

The day-long hearing, convened by the National Transportation Safety Board, provided dramatic accounts of how five people survived the accident. But much of the testimony concerned technical questions, particularly theories that the jet took off heavily laden with ice or snow which caused faulty instrument readings and damaged the wings' ability to lift.

The hearing also made clear that investigators have closed many earlier paths of inquiry. The plane's pilots were qualified and medically fit, chief investigator Rudolph Kapustin said in an opening statement. Its engines, body and systems appear to have been in good repair, and there is "no evidence of any pre-existing, uncorrected problems with the airplane related to its performance capability," Kapustin said. He said, however, that the possibility of damage to certain control surfaces is still under study.

Testimony and documents released yesterday at the hearing indicated:

Pilots of the 737 put their engines in reverse at least twice while taxiing for take-off. Boeing, the plane's manufacturer, has warned against using reverse thrust while snow is falling, because it can refreeze snow as solid ice on wing surfaces.

A passenger aboard an Eastern Airlines plane that taxied by the Air Florida 737 as it was parked at its gate photographed the plane. His photo, somewhat unclear due to the snowfall, appears to show snow on the fuselage. The passenger said he took the picture sometime between 3:19 and 3:24 p.m., after the Air Florida plane had received its final de-icing treatment.

An investigation document said that another Eastern jet may have touched down on Runway 36 before the Air Florida jetliner had lifted off the other end. Though investigators do not believe that the Eastern plane figured in the accident, they note that two jets on a runway simultaneously would be a serious safety hazard in its own right.

Analysis of radar data and air traffic control tapes indicate that Eastern Flight 1451 touched down at either 28 or 31 seconds after 4 p.m, though investigators cautioned that the equipment has a significant margin for error.

Transcripts of the Air Florida plane's cockpit voice recorder indicate that that jet was still on the runway and had just reached its "go/no-go" speed at 31 seconds after 4 p.m.

The position of flight attendants at the time of take-off violated Air Florida regulations, with two at the front of the cabin, and one, Kelly Duncan, in the rear by the door. Two attendants are supposed to sit by the rear door to assist in any evacuation, a Federal Aviation Administration official said.

The Air Florida jet was de-iced twice during heavy snowfall as it awaited permission to leave its gate. All three survivors yesterday said they were aware of the de-icing, performed by American Airlines employes who sprayed water and ethelene glycol solution over the plane.

Patricia Felch, who arrived at the hearing room in a wheelchair, said that the plane's left wing was de-iced only the first time and snow quickly began to accumulate on it afterwards. "I turned to my boss Joseph Stiley, another survivor and said 'they're going to have to de-ice this again.' " Stiley and the fifth survivor, Priscilla Tirado, did not testify yesterday because of medical problems.

When the jet had trouble pulling away from the gate, according to Felch and other witnesses, the pilots put its engines into reverse thrust for 30 to 90 seconds to try to break it loose. A tractor operator told investigators that he had advised the pilots that doing so violated regulations. Felch said the pilots reversed thrust again while taxiing.

At about the same time, two ground crewmen who saw the jet leave the gate "engaged each other in a conversation as to why Air Florida was allowed to take off with large accumulations of snow," which they said was mostly on the rear of the fuselage, according to a document released yesterday.

In other testimony, pilots at National that day said they saw snow or ice on the plane before it took off. One report quoted a pilot as remarking to his fellow crew-members, "Look at the junk on that airplane." Other pilots have said, however, that they did not see any snow on it.

Transcripts from the Air Florida jet's cockpit voice recorder show the two pilots, Larry Wheaton and Roger Alan Pettit, joked about the heavy snowfall that day. Based on the tape, some investigators believe that the two knew they had ice or snow or the wings but took off anyway, breaking federal regulations.

All three survivors said take-off seemed disturbingly different. Duncan said the engines were not as loud as usual. Felch said "it wasn't the same force in the sensation that you have of being pushed back in your seat . . . I thought the pilot would abort the flight." Hamilton said the run seemed longer than usual and the climb not as steep.

This testimony seemed to buttress theories that frozen sensors caused the crew to set their throttles too low.

All three said that violent shuddering beginning after the plane lifted off. Airframe vibration is a sign that a plane is stalling, or falling out of the air because its wings are not generating enough lift.

Felch said she saw tree tops out her window and crouched in her seat. "I remember a severe jolt," as the plane hit the bridge, then that "there was water around my ankles and that it was quickly filling up." She struggled to free her feet and undo her seat belt in the dark. Then "it seemed like we went straight up."

The survivors swam to the wreckage, with Duncan recalling that she had to push chunks of ice out of the way. Investigators showed interest in accounts that they were unable to remove the one life jacket they had from its bag. Both Felch and Duncan claimed responsbility for tearing the plastic bag open with their teeth.

Hamilton said the helicopter dropped a life-saving device that was meant to inflate on impact. But it did not and he pushed it away, thinking "what good is this thing?" Hamilton recalled yelling to people on the bridge: "What we need are boats, get a boat out here."