Authorities today gave up hope of finding survivors in the crash of EgyptAir Flight 990, but Coast Guard search crews found a large piece of wreckage and heard what may be a radio signal from one of the aircraft's flight recorders.

Only a day after the jetliner plunged into the Atlantic off the coast of Massachusetts, National Transportation Safety Board officials said the possible discovery of at least one of the plane's "black boxes" gave a spark of hope to what otherwise will be a long and difficult investigation.

NTSB Chairman Jim Hall said today that nothing has been ruled out as a possible cause of the crash, and the FBI is continuing to review lists of passengers, maintenance crews and others who had contact with the aircraft. The bureau also is bringing lab and bomb technicians to the scene to assist in the investigation.

Among the passengers on the downed plane were 30 members of an Egyptian Defense Ministry delegation, including two generals, who U.S. officials said had been in the United States discussing helicopter contracting issues. Passengers also included 32 other Egyptians, 106 Americans, 22 Canadians and people of several other nationalities.

The Boeing 767 plunged from 33,000 feet into the Atlantic early Sunday without a distress call from the crew--making an unusually steep dive of 23,200 feet per minute and falling to 19,100 feet in 36 seconds, according to preliminary radar data. The plane's transponder stopped operating and reporting altitude at that point.

Hall cautioned that even if crews quickly recover the black boxes, information about the crash would still be slow in developing because the wreckage is located in about 250 feet of water--twice the depth of the wreckage from the 1996 crash of Trans World Airlines Flight 800--thus limiting diving at the site. High winds and strong rains were predicted to hit the search area Tuesday afternoon, and sophisticated Navy search ships were still on their way to the site, making a swift recovery of bodies and wreckage unlikely.

Still, searchers found what investigators described as a large piece of the aircraft that will require a crane to remove it from the water. Crews also have collected an assortment of clothing, purses and other personal items of passengers, but so far none of it has any burn marks that might indicate a fire or explosion, investigators said. The Coast Guard planned to continue its search before undersea recovery using Navy ships begins.

"Factual information may not be developed as fast as the press may like," Hall said at a briefing. He added that the recovery of bodies "may be more extended than before."

This is more bad news for family members of the 217 passengers and crew who died on the plane, which took off at 1:19 a.m. EST Sunday from John F. Kennedy International Airport in New York for Cairo. It disappeared from radar at 1:52 a.m. EST.

The potential good news is that investigators may be on the track of one of the two black boxes from the 767. A cutter heard the telltale "pinging" signal today, but Hall said it will be at least 36 hours before ships will be on scene and ready to pinpoint the signal and possibly begin recovery operations.

Recovery of the cockpit voice recorder and the flight data recorder is particularly important because the plane and its crew provided few other clues.

Data from other nearby radars have been recovered and are being analyzed, Hall said. If they confirm the preliminary data from the original radar, it is possible that the plane remained relatively intact and under power down to the 19,100-foot level and broke up at that point. It is far too early to make that determination, however.

Refined data could determine whether smaller pieces left the plane before it made its dive, indicating either the start of a structural breakup or an explosion of some sort.

Investigators also may explore whether some type of mechanical failure involving the thrust reverser or some other system came into play.

The plane involved in Sunday's crash was built in September 1989. It came off Boeing's Everett, Wash., assembly line about two weeks before a 767 that crashed in a jungle in Thailand in May 1991, killing 223 on board.

EgyptAir's 767 was the 282nd built by the company, while the plane involved in the Thailand crash, operated by Lauda Air, was number 283.

The Lauda Air 767 had just taken off from Bangkok and had climbed to 10,000 feet when the thrust reverser, an engine braking device, accidentally deployed, causing one of the plane's two jet engines to pull the aircraft into a fatal dive.

In 1994, three years after the Lauda crash, the Federal Aviation Administration ordered a series of major thrust-reverser fixes for all U.S.-registered 767s. Foreign carriers, like EgyptAir, typically abide by such FAA-mandated upgrades, though they are not strictly required to do so.

The EgyptAir 767 did undergo that modification, the airline's vice president for technical affairs, Maged Masri, told the Associated Press today. He said the modification was made in 1993 at a British Airways workshop in London.

Safety board investigators today were getting organized for the probe, which chief investigator Greg Phillips said would evolve over "the coming months and maybe years." In addition to radar data and recovery efforts, investigators will comb maintenance files, weather and other information and will interview anyone who might be able to offer clues to the competence and mood of the crew.

An Egyptian investigative team was to join U.S. investigators Tuesday at the command center at the Quonset Point Naval Base near here.

Some of the most sophisticated recovery ships in the world were sailing toward the crash site about 60 miles south of Nantucket Island, including the Navy recovery ship USS Grapple, which was a key to recovery of TWA 800 wreckage through use of side-scanning radar to map the ocean floor and modern salvage equipment, including an unmanned recovery vehicle.

A Navy spokesman said the Grapple will be equipped with gear to allow longer and deeper dives.

Several other vessels from the Coast Guard and the National Oceanic and Atmospheric Administration were to join in the recovery effort with six Coast Guard cutters now on scene.

Staff writers Bradley Graham, David A. Vise and John Lancaster in Washington contributed to this report.

CAPTION: Soheir Makary, center, whose brother died aboard EgyptAir Flight 990, walks with cousin Adel Shehata, left, to a plane at Kennedy Airport bound for Providence, R.I.

CAPTION: Coast Guard vessels return from the EgyptAir Flight 990 crash area off the Massachusetts coast. Sophisticated recovery ships are en route to the site.