at would have been a safe seat for the Republicans if he had chosen to run again. His departure gives Democrats a better chance to protect or even expand their one-seat majority in the Senate.

Warner said he still feels spry enough for the rigors of the Senate, but he did not want to push it for another six years.

"I want to be fair to this wonderful state, which has been eminently fair to me all these years," Warner said.

His message to Virginians, he said, is: "You've given me my best shot, and I'm quietly gong to step aside and make way for others."

Warner, former chairman of the Senate Armed Services Committee, has long been an important voice in the Iraq debate because of his military expertise and his willingness to question White House war policy.

After a recent trip to Iraq, Warner said President Bush should start bringing some troops home by Christmas. If Bush refused, Warner said, he would consider backing anti-war legislation. The statement was the senator's strongest to oppose the White House and is expected to influence the Iraq debate this fall.

Warner, a courtly senator with chiseled features and a full shock of gray hair, chose a sentimental setting for his announcement: the steps of the University of Virginia's signature structure, the Rotunda, designed by school founder Thomas Jefferson. Warner graduated from the university's law school in 1953.

The most likely Democratic contender is former Gov. Mark R. Warner, a wealthy Alexandria businessman who left office in early 2006 with unprecedented job-approval ratings. Mark Warner, who is not related to the senator, unsuccessfully challenged him in the 1996 Senate race.

The nomination battle among Republicans probably will include former Gov. Jim Gilmore and U.S. Rep. Thomas M. Davis.

The GOP nominated Warner for the Senate in 1978 after the party's first choice, Richard Obenshain, was killed in a plane crash. Warner was elected by just 4,721 votes out of 1.2 million cast. He was easily re-elected in 1984 and 1990. He beat Mark Warner by 5 percentage points in 1996 and was unopposed in 2002.

"Public service is a privilege and I urge all to try to find time some time in their lifetime to serve the needs of others," Warner said Friday. "I have tried to be not only true to myself, but true to the people of this great commonwealth I've served for 29 years now."

Sen. Hillary Rodham Clinton said she will miss her "friend and colleague."

"At a time when the tone in Washington is so often defined by partisanship and rancor, Senator Warner has always risen above the fray," Clinton said.

In 1996, the conservative wing of his own party tried to deny Warner a fourth term. Warner had angered conservatives two years earlier by opposing GOP nominee Oliver North's bid to unseat Democratic Sen. Charles S. Robb. Warner declared the Iran-Contra figure unfit for public office and backed an independent who drew enough votes from moderates to ensure Robb's re-election.

Angered by what they viewed as party disloyalty, GOP conservatives backed former Reagan administration budget director Jim Miller to challenge Warner for renomination. Warner easily defeated Miller in a primary.

Warner mended his relationship with the GOP by supporting the successful campaigns of Gilmore for governor in 1997 and George Allen for Robb's Senate seat in 2000.

Gov. Timothy M. Kaine, a Democrat, called Warner "a good friend, a great Virginian, and a true statesman."

"All Virginians should honor his distinguished leadership," Kaine said.

Warner is Virginia's second-longest serving senator, with a tenure surpassed only by that of Sen. Harry F. Byrd Sr., who held office from 1933 to 1965.

Warner's actions in recent weeks had fueled speculation that he would retire. Several longtime staff aides and advisers moved on to other jobs, and he raised less than $75,000 in campaign money for the first half of 2007, including only $500 in the first three months.

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