Arlington would still be home to the Pentagon. But in losing thousands of civilian defense workers and private contractors, the county also would lose some of its identity.

In the prosaic, boxy office buildings of Crystal City and Ballston and Columbia Pike, some of the world's smartest scientists, researchers and analysts have developed some of the most powerful and deadly weapons. Some have devised maps from satellites and divined intelligence. Others simply have balanced the Army's books.

Arlington, which along with Alexandria could lose more than 20,000 defense-related jobs as a result of the Base Closure and Realignment Commission vote yesterday, was named in 1920 after the estate of a Civil War general. World War II transformed it from a sleepy farm community to an urban center, bustling with workers and a sense of national purpose.

Now, it could have to remake itself.

"We've had a long history with the Department of Defense," said Jay Fisette, chairman of the Arlington County Board. "This is a mixed bag for us."

Mixed, he said, because there could be some initial hardship. People would move. Families would be uprooted. Traffic and the resulting air pollution probably would get worse, as thousands of jobs move south to the self-contained Fort Belvoir in Fairfax County and the Quantico Marine Corps base in Prince William. Office space in Northern Virginia would be vacant and cheaper.

And mixed, he said, because that cheaper office space would fill with other businesses, which could revitalize and reinvigorate such places as the demi-skyscrapers and empty streets of Crystal City, which could be described as sterile at best. "This gives property owners a chance to upgrade," Fisette (D) said. "It creates more opportunities."

In an ironic way, Fisette and other Northern Virginia officials predicted that the decision to move so many defense jobs outside the Beltway might draw far-flung, outside-the-Beltway businesses closer in.

U.S. Rep. James P. Moran Jr. (D-Va.) represents the Northern Virginia area that is slated to lose jobs and the area of Fairfax where they would be moved, which is set to boom. He foresees short-term pain over the forced change of character around the Pentagon. Yesterday's move was the equivalent of four major base closings, he said, and repercussions would be regionwide.

"There won't be tumbleweeds in Crystal City," he said. "Because of Arlington's proximity to D.C. and being on a Metro line, this space will fill right up."

Moran described the defense work in Arlington as the brains behind the military. And, after intense lobbying, Virginia lawmakers persuaded commissioners to leave some of the top defense research agencies right where they are.

Commissioners voted to allow the Defense Advanced Research Projects Agency and the Office of Naval Research -- which is in the process of moving into a new, $12 million building in Ballston -- to stay.

In town hall meetings this summer, Moran found that as many as half the scientists and researchers in these agencies -- people who easily could work in the private sector -- did not want to move.

"I'll flip hamburgers in Arlington before I'll commute to Bethesda," Thomas F. Hafer, a contractor who works with the Office of Naval Research, said at a June meeting.

In Crystal City yesterday, Rodney Millner, 52, a Defense Department analyst who lives in Laurel, said he would move to Virginia if his job were transferred to Fort Belvoir. But he said he doesn't expect his one-hour-20-minute commute to get shorter. "If everybody's moving there, there'll be just as much traffic," he said.

Moran said he would work to get federal money to deal with traffic congestion and other problems associated with moving so many people at once to southeastern Fairfax.

Fairfax officials said they are not against a new community in their county of more than 1 million people. They're opposed to finding themselves unprepared for 18,000 additional people on the roads near Fort Belvoir and for thousands of children looking for spots in schools that are already at capacity. "We will do the best we can to welcome those people," said Supervisor Gerald W. Hyland (D-Mount Vernon), who represents the area around Fort Belvoir, which is growing faster than any other spot in the county. "But we will be looking to our federal partners to help us."

Despite the vote, Virginia lawmakers said they will not concede defeat. The plan will go to Congress for approval and to various committees for money to fund the job transfers. "We get another crack at that down the road," said U.S. Rep. Thomas M. Davis III (R-Va.). "There are several other ways to attack this thing."

During the base closure hearings, local lawmakers and officials made no secret that they felt unfairly targeted by the Pentagon, which adopted rules requiring leased buildings to be set back 82 feet from traffic and prohibiting them from sitting atop Metro lines or parking garages. None of the buildings in Arlington -- or any urban area, really -- meets those standards. The idea is to prevent terrorist truck bombs or attacks from below.

Moran and others said the Pentagon used these standards to flush jobs from inside the Capital Beltway.

"Terrorists had no idea what all these leased office facilities were," Moran said. "They didn't even know what the acronyms stand for. The Pentagon's the target, and the target's not moving."

Staff writers Lisa Rein, Michael D. Shear and Lila de Tantillo contributed to this report.