"The area of the Pentagon where the aircraft struck and burned sustained catastrophic damage. Anyone who might have survived the initial impact and collapse could not have survived the fire that followed," the Defense Department said in a written statement.

Arlington, Va., fire officials involved in the search and rescue estimated that 100 to 800 people may have died.

J.H. Schwartz, assistant fire chief for Arlington, said rescuers had pulled about 80 bodies from the building so far but it was too early to know how many more could be retrieved Wednesday.

"We want to assure that we have a safe working environment for the firemen going into that building," Schwartz said.

Only about half of the massive building, struck Tuesday by a hijacked American Airlines jet, had power. Many of the 24,000 employees were asked not to come to work.

Smoke billowed from the damaged and collapsed areas on the southwestern side of the building, drifting over the northern Virginia skyline. Jet fuel had caused an intense fire.

The Pentagon said nobody in the vicinity of the impact could have survived and listening devices haven't discovered signs of life.

U.S. officials held out the hope that some people might be found in adjacent areas after a wrecking ball is used to clear unstable rubble.

Teams of a dozen rescuers are equipped with dogs that can differentiate between bodies and live victims; acoustic listening devices that can pick up the faintest sound; and sophisticated cameras.

Around the area of impact along the building's perimeter, where a section of the building collapsed, FBI evidence teams found parts of the fuselage from the Boeing 757, Tamillow said. No large pieces apparently survived.

Agents also were looking for the plane's flight-data and cockpit voice recorders.

Air inside the Pentagon was tinged with the scent of an electrical fire. In corridors where workers gathered, water and electricity, phone lines and computers were in full use.

But many corridors ended in blacked-out hallways. Yellow tape and Defense Department policemen warned people away.

The plane smashed a 35-foot area across five floors. The aircraft entered the building in the wedge between two corridors, collapsing the outermost ring of the building.

Pentagon officials asked workers in surrounding corridors not to enter their offices because of structural damage.

The chairman of the Joint Chiefs, Army Gen. Henry H. Shelton, was in his office early Wednesday, as was Defense Secretary Donald H. Rumsfeld, officials said.

In the air around the Pentagon, helicopters frequently landed and took off. Military trucks and jeeps went by in convoys. Ambulances and firefighting equipment ringed the area.

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Associated Press writer Susanne M. Schafer contributed to this report.

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