Democratic Sen. Evan Bayh of Indiana will not seek the presidency in 2008, saying he believes the odds of a successful run were too great to overcome.

"At the end of the day, I concluded that due to circumstances beyond our control the odds were longer than I felt I could responsibly pursue," Bayh told the Indianapolis Star. "This path — and these long odds — would have required me to be essentially absent from the Senate for the next year instead of working to help the people of my state and the nation."

The announcement comes just two weeks after Bayh, in an appearance on a Sunday talk show, announced that he would take a first step toward a 2008 presidential campaign by forming an exploratory committee. His decision to step aside narrows a field dominated by Whites House hopefuls, Sens. Hillary Rodham Clinton of New York and Barack Obama of Illinois.

Just last weekend, Bayh traveled to New Hampshire, the early presidential primary state, but his appearance was barely noticed as Obama delivered two speeches to sold-out crowds and drew hordes of media. Bayh is the second well-known Democrat to decide against a 2008 run; former Virginia Gov. Mark Warner announced earlier that he wouldn't pursue the presidency.

"The odds were always going to be very long for a relatively unknown candidate like myself, a little bit like David and Goliath," Bayh said in a statement on the newspaper Web site. He added that beyond the question of "whether there were too many Goliaths or whether I'm just not the right David," his chances were slim.

Bayh, 50, also left open the possibility of another run, saying, "There may be no campaign in the near future, but there is much work to be done."

Bayh is a Democrat with a record of political success in a Republican-leaning state. He had been pointing toward a run for the White House for months, and had $10.5 million in his Senate campaign bank account as of Sept. 30. Money that could be transferred to his exploratory committee.

In addition, the senator recently hired his first paid organizer for Iowa, the state whose caucuses will be the opening competition of the campaign.

Among the announced Democratic candidates are Iowa Gov. Tom Vilsack and Ohio Rep. Dennis Kucinich, but Clinton and Obama loom large in a potential field that also could include 2004 vice presidential nominee John Edwards, New Mexico Gov. Bill Richardson and former Sens. John Kerry of Massachusetts, Joe Biden of Delaware and Chris Dodd of Connecticut. The Republican lineup is equally crowded with Sen. John McCain of Arizona, former New York City mayor Rudy Giuliani and Massachusetts Gov. Mitt Romney.

As a member of the Senate Intelligence and Armed Services committees, Bayh was one of the first Democrats to support military action in Iraq. But in December 2005, he changed his position, saying he would not have supported legislation authorizing the invasion if the facts the Bush administration used to support the move had been presented to him accurately.

Bayh has charted a centrist's course throughout his political career, including two terms as governor and eight years in the Senate. He also has served as chairman of the Democratic Leadership Council, which is a prominent voice for moderation within the party, and has helped establish the centrist New Democrat Coalition.

Elected governor in 1988, he was the first Democrat in 20 years to hold that office and — at 33 — the youngest state chief executive in the United States.

Bayh was often referred to as a "Republicrat" who courted the middle. He never raised taxes and he left office with a humming state economy, low unemployment and a record budget surplus.

His approval rating was an astonishing 79 percent in a state that hasn't voted for a Democratic presidential nominee since Lyndon Johnson's 1964 landslide.

He drew national notice, too, as his tenure neared an end. Bayh was tapped to give the keynote address at the 1996 Democratic National Convention.

He was elected to the Senate two years later.

In recent years, Bayh voted against confirmation of Chief Justice John Roberts as well as Supreme Court Justice Samuel Alito; opposed legislation to open a portion of an Arctic wildlife refuge to oil drilling; supported a comprehensive immigration bill that included a path to citizenship for millions of men and women in the country illegally.

Bayh is the son of Birch Bayh, who won three terms in the Senate from Indiana before losing his seat to Dan Quayle in the Republican landslide of 1980.