Salvage workers recovered the tail section of the Air Florida jetliner from the Potomac yesterday only to find that the electronic devices federal investigators hope will provide vital clues to the cause of the crash were not in it.

"The recorders were not in the tail section," said National Transportation Safety Board member Francis H. McAdams. "At this point we don't know what happened."

McAdams, one of the five members of the federal committee investigating Wednesday's crash of a Boeing 737 that killed 78 persons, said it is possible the devices dropped out when the tail section was lifted from the water.

Reporters on the 14th Street bridge near the crash site saw substantial parts of the wreckage tear loose and drop back into the river as a crane lifted the mangled tail first onto a pair of steel barges and then up onto the bridge itself.

The devices investigators are eager to recover are the cockpit voice recorder and the flight data recorder. The voice recorder records all cockpit conversation. The flight data recorder registers information about the performance of the aircraft and is an essential aid for air crash investigators.

Crash investigators said last week that divers using sonar had been able to pick up signals emitted from so-called "pingers," water-activated, battery-powered transmitters that are mounted on the outside of the bright orange recorders.

Divers went back into the water after the tail section was recovered. McAdams said they detected "two distinct and separate pinging sounds." The sounds, McAdams said, seemed to be coming from the area where the tail section had been in the river. The divers suspended operations at 6:15 p.m. and will resume in the morning.

In 737s, the cockpit voice recorder, which measures about 5 by 8 by 12 inches, is located under the floor of the cabin about four windows forward from the tail. McAdams said the fuselage apparently split just where the voice recorder would have been. The flight data recorder, slightly larger at about 5 by 8 by 22 inches, would have been just above the rear door, the galley door, of the aircraft.

The federal government has required for about 20 years that airliners carry the boxes, ever since high speed jet aircraft came into general use and crashes tended to leave the airplane less intact. The idea is to provide an objective record of what happens before a plane hits.

Besides recovering the tail section, which was to be taken by truck to a hangar at National Airport where the investigating committee is assembling the recovered parts of the aircraft, the divers also brought up seven more bodies. Of the 78 persons killed in the crash, the bodies of 53 from the airplane and four killed when the plane struck the bridge have been recovered.

McAdams said that a consensus was forming among the witnesses interviewed that the plane's nose was up at 30 degrees on takeoff. Given the conditions prevailing at the time, McAdams said, an angle of about 15 degrees would have been correct.

At least one passenger and some witnesses have reported that the plane appeared to remain too long on the runway attempting to gather speed before it actually took off. The angle at which the plane took off is expected to be an issue in the investigation. Attempting to climb too steeply lacking sufficient speed could force a plane into a stall.

Investigators also were able yesterday to make contact with a cabdriver whom they had been seeking, McAdams said. Contrary to earlier reports, the cabdriver did not see the plane taking off, but saw it when it was at an altitude of about 150 feet. The cabdriver, who is also a private pilot, McAdams said, estimated the nose angle to be about 30 degrees up and reported that the landing gear was still down.

Among the bodies recovered may be that of the anonymous victim who handed a lifeline to four fellow passengers, passing up a chance to save himself. The man drowned before rescue workers had a chance to pull him out.

National Park Service spokesman Sandra Alley said it was "a good possibility" that Arland Williams, 46, was the person who saved the four passengers, but cautioned that two dozen bodies remain in the Potomac River and that no final determination will be made of the person's identity until all the victims have been recovered. Williams was a directing bank examiner for the Federal Reserve Bank in Atlanta.

Williams was balding and had a salt-and-pepper mustache and beard, the same general description given by the two crew members of a Park Police helicopter who witnessed the man's efforts. Williams also is the only one of the 53 victims recovered so far from the aircraft who died of exposure and drowning, according to the D.C. medical examiner's office. The rest died from the impact of the crash.

D.C. police released the names of five of the seven persons whose bodies were recovered yesterday and a sixth person whose body was recovered Saturday. The five are Chalmers McIlwaine Jr., 42, of Great Falls, Va.; Robert Silberblied of Boston; Stanley Woodard, 77, of Silver Spring; Jack Viehman of Washington, and Cathy Delmonte of Virginia. In addition, the body of Dorothy Stemper of Washington has been identified.

Although witnesses to the crash reported seeing two cars swept into the river by the plane, Delaplane said Sunday that divers have searched the area near the bridge and have found no indication that cars are in the river. Two bodies of persons who were in cars have been recovered from the river.

Kelly Duncan, the 23-year-old Air Florida stewardess who was one of only five persons aboard the plane to survive the crash, was discharged yesterday from the National Hospital for Orthopaedics and Rehabilitation in Arlington. In addition to suffering from hypothermia from the near-freezing water, she sustained a broken ankle. The four other survivors are still hospitalized, but listed in good condition. In addition, one person injured on the bridge by the plane is still hospitalized.

Duncan left with her parents and sister to catch a plane at National Airport, according to a hospital spokeswoman. Duncan, the spokeswoman said, told her that she doubted that she would be returning to flying as a career.