Adds more details from press conference in paragraphs 2, 4-10

By David Shepardson and Jonathan Allen

WASHINGTON, Feb 2 (Reuters) - Officials have positively identified 55 of the 67 people killed in Wednesday's midair collision between an American Airlines AAL.O passenger jet and a military helicopter over the Potomac River in Washington, D.C.

"It's my belief that we're going to recover everyone," Fire Chief John Donnelly said on Sunday at a press conference. "We have some work to do as the salvage operation goes on."

On Monday, the Army Corps of Engineers will begin lifting the wreckage from the river, which officials have said could take a week or longer.

"We have a wide debris field," said Colonel Francis Pera of the U.S. Army Corps of Engineers. "Within that wide debris field, we're employing different techniques to make sure we can understand what's in the water."

Work will be halted as remains are discovered during removal operations, officials added.

Earlier on Sunday, relatives of the 67 people killed arrived at the edge of the river near the crash site on buses.

Wreckage is being moved to a hangar at Washington Reagan National Airport. Much of the Potomac River remains restricted to authorized vessels. Two of the lesser-used runways at the airport remain closed.

Investigators from the National Transportation Safety Board said Saturday they had determined the CRJ-700 airplane was at 325 feet (99 meters), plus or minus 25 feet, at the time of impact.

The information was based on data recovered from the jet's flight data recorder - the "black box" that tracks the aircraft's movements, speed and other parameters.

The new detail suggests the Army helicopter was flying above 200 feet (61 meters), the maximum altitude for the route it was using.

Data confirms the air traffic controller alerted the helicopter to the presence of the CRJ-700 about two minutes before the crash.

One second before impact, the American flight crew had a "verbal reaction," according to the plane's cockpit voice recorder, and flight data shows the plane's nose began to rise, officials said.

(Reporting by David Shepardson and Jonathan Allen; Editing by Sandra Maler and Lisa Shumaker)

((David.Shepardson@thomsonreuters.com; 2028988324;))