ALEXANDRIA, Va.— Senator Allen, a Republican, gracefully conceded defeat yesterday after a bruising battle against Democrat Jim Webb, sealing the Democrats’ control of Congress and the political downfall of a man once considered a White House contender.

Mr. Allen said the “owners of government have spoken, and I respect their decision.”

“The Bible teaches us there is a time and place for everything, and today, I called and congratulated Jim Webb and his team for their victory,” he said.

A former Republican and Navy secretary under President Reagan, Mr. Webb, claimed victory early Wednesday after election returns showed him with a narrow lead of about 7,200 votes out of 2.37 million ballots cast.

Mr. Allen chose not to demand a recount when initial canvassing of the results failed to significantly alter Mr. Webb’s lead.

“I see no good purpose being served by continuously and needlessly expending money and causing any more personal animosity,” he said. “Rather than bitterness, I want to focus on how best Virginians can be effectively served by their new junior senator.”

The Virginia contest was the last undecided Senate race in the country, and Mr. Webb’s victory tipped the scales, giving the Democrats control of 51 Senate seats and majorities in both the House and Senate for the first time since 1994.

Earlier in the day, Senator Burns conceded the Montana Senate race to Democrat Jon Tester, catching Mr. Tester on the phone as he headed for a barber shop to get his famous flat-top hair trimmed.

The call was “very cordial, very professional. It was positive,” Mr. Tester, who is a farmer and state legislator, told the Associated Press.

A three-term GOP senator whose campaign was troubled by gaffes and voter discontent, Mr. Burns made no public appearances. But he released a written statement saying he was ready to “help as Montana transitions to a new United States senator.”

“We fought the good fight, and we came up just a bit short. We’ve had a good 18 years, and I am proud of my record,” he said.

In the Virginia race, Mr. Allen had been expected to cruise to a second term this year and make a run for the White House in 2008. The son of a Hall of Fame football coach, Mr. Allen served as governor in the 1990s and was popular for abolishing parole and instituting other conservative reforms.

But, in Mr. Webb, he faced an unconventional challenger. Supporters drafted Mr. Webb, who is a political neophyte, to run because of his early opposition to the Iraq war.

Mr. Allen, 54, was comfortably ahead in polls until August, when he mockingly referred to a Webb campaign volunteer of Indian descent as “macaca,” regarded by some as a racial slur. The incident, caught on videotape, became international news. Some former football teammates from the University of Virginia also charged that Mr. Allen had commonly used a slur for blacks — something he denied.

Mr. Webb, a 60-year-old Naval Academy graduate and decorated Vietnam veteran, tried to tie Allen to President Bush and the war during the campaign. He also seized the Reagan edge, having served in the former president’s administration, and used a video in ads that showed Reagan praising him.