Recovered from the hijacked plane that slammed into the building Tuesday were the damaged voice recorder and the charred flight data recorder. They were sent to the FBI, and officials were hopeful the two ''black boxes'' would provide clues about the final moments of American Airlines Flight 77.

The Army announced the names of 74 people unaccounted for since the attack. Government authorities said 190 people - a combination of military and civilian employees on the ground and the passengers in the plane - were believed to have died.

''We are in pain but, but we are also angry,'' said Army Chief of Staff Gen. Eric K. Shinseki at a news conference with Army Secretary Thomas E. White.

''September 11 has already been described ... as the darkest day in American history,'' White said. ''I would only say to our adversaries that I would learn to watch carefully for you're about to see our finest hour in the near future.''

Earlier, at a prayer service, men and women wiped away tears as they sang ''God Bless America.''

''My heart pains for you and I pray that God will comfort you,'' Army Maj. Gen. Robert Van Antwerp Jr. told them.

Van Antwerp, assistant chief of staff for installation management, said that his secretary and administrative assistance were killed. He was at a meeting outside the Pentagon on Tuesday when the plane attacked the huge five-sided building.

''I am experiencing some of the same emotions that many of you are,'' he told 250 people in an auditorium and an overflow crowd watching from a television hallway. From a window, rescue cranes could be seen stretched skyward over a roof section scattered with debris.

In a nearby hallway, workers wearing paper surgical masks washed soot from the walls and floors.

Outside, rescue and recovery workers continued to go through debris from crash.

''You feel grieving for ... the soldier who has fallen,'' said Sgt. Brock Bowman of Olympia, Wash., helping put bodies into bags as rescue workers retrieved them from the rubble. ''You also feel some anger, and this is justified.''

''It makes you realize your own mortality,'' said one rescuer, Sgt. John Trotter, 21, of San Antonio.

Trotter and Bowman are members of the Army's Old Guard of the Military District of Washington. The unit normally performs ceremonial duties, including at the White House and Arlington National Cemetery's Tomb of the Unknown Soldier.

On Friday, they were putting remains into bags and onto refrigerator trucks.

About one-third of the 6 million square foot building is unusable because of the collapse of the section where the plane hit and because of the ensuing fire and water damage, said John F. Irby, director of federal facilities.

He said repairing the destroyed areas would take several years and cost more than $100 million but less than $1 billion. ''We took a big hit,'' Irby said.

Air sampling showed that levels of asbestos, carbon monoxide and other toxins were at safe levels in occupied parts of the Pentagon and some 350 people were working to clean the soot from the building, Irby said.

Search and rescue teams continued to work to stabilize the damaged section. Recovery efforts were complicated by a brief but heavy rain Friday.