WASHINGTON - The subway train that plowed into another stopped train, killing at least seven people and injuring scores of others in the nation's capital, was part of an aging fleet that federal officials had sought to phase out because of safety concerns, an investigator said today.

But the Metrorail transit system kept the old trains running despite warnings in 2006, said Debbie Hersman of the National Transportation Safety Board.

The rush-hour crash sent more than 70 people to hospitals. Mayor Adrian Fenty announced today that seven had died, including the operator of the moving train. Earlier, the District of Columbia Fire Department Web site announced that three bodies had been found in addition to the six fatalities reported Monday.

Fenty said two victims were hospitalized in critical condition.

Hersman said investigators expect to recover recorders from the train that was struck. The train that triggered the collision was part of an old fleet that was not equipped with the devices, which can provide valuable information to determine why the crash occurred, Hersman said.

She told The Associated Press that the NTSB had warned of safety problems and recommended the old fleet be phased out or retrofitted to make it better withstand a crash. Neither was done, she said, which the NTSB considered "unacceptable."

It was the worst crash in the history of Metrorail, the pride of the District of Colombia tourism industry that has shuttled tourists and commuters around Washington and to Maryland and Virginia suburbs for more than three decades.

The operator of the train that barreled into the stopped cars was identified as Jeanice McMillan, 44, of Springfield, Va., according to Metro officials.

McMillan was hired in March 2007 as a bus driver and was tapped to become a train operator in December. Metro spokeswoman Candace Smith said employees start out as bus drivers before moving to trains.

One of McMillan's neighbors said she was proud of her job and was a meticulous mother who ironed her uniform every night.

"If she could have stopped the train, she would have done everything in her power," said Joanne Harrison, who lives across the hall from McMillan.

She put a note, decorated with purple ribbons and hearts, on McMillan's door.

"Your friendly smile and your appealing welcome will always be dear to our hearts," the note said. "Don't you worry, we will take care of Jordan, your only child, your only love."

Passenger Maya Maroto, 31, was riding on McMillan's train.

"We were going full speed - I didn't hear any braking. Everything was just going normally. Then there was a very loud impact. We all fell out of our seats. Then the train filled up with smoke. I was coughing," she said.

Maroto, of Burtonsville, Md., said there was confusion after the impact because no announcements were immediately made. She said some passengers wanted to climb out, but others were afraid of being electrocuted by a rail.

Tijuana Cox, 21, was in the train that was hit. She had her sprained arm in a sling today.

"Everybody just went forward and came back," with people's knees hitting the seats in front of them, said Cox, of Lanham, Md.

The only other fatal crash in the Metro subway system occurred Jan. 13, 1982, when three people died as a result of a derailment. That was a day of disaster in the capital: Shortly before the subway crash, an Air Florida plane slammed into the 14th Street Bridge immediately after takeoff from Washington National Airport. The plane crash, during a severe snowstorm, killed 78 people.

In January 2007, a subway train derailed in downtown Washington, sending 20 people to the hospital and prompting the rescue of 60 others from the tunnel. In November 2006, two Metro track workers were struck and killed by an out-of-service train. An investigation found that the train operator failed to follow safety procedures. Another Metro worker was struck and killed in May 2006.