WASHINGTON – In a surprise decision that reconfigures the race for the 2008 Democratic presidential nomination, former Virginia Gov. Mark Warner announced Thursday that he would not run, saying he was unwilling to put his family second to a presidential campaign.

Warner, a centrist Democrat from a Republican-leaning Southern state, was considered by many Democratic strategists to be the strongest potential rival to Sen. Hillary Clinton, D-N.Y., the early front-runner for the nomination.

His decision opens the field for other candidates hoping to present themselves to voters as centrists, including Sen. Evan Bayh, D-Ind., Iowa Gov. Thomas Vilsack, and New Mexico Gov. Bill Richardson.

“The great dynamic in this race is: Who are the one or two others in the pack who can break out and challenge Senator Clinton?” asked Simon Rosenberg, founder of the New Democrat Network, an organization that promotes progressive Democratic candidates. “This benefits all the people who are going to be challenging Hillary.”

Warner’s stature among the field of Democrats was based less on his nationwide popularity – he polled in the single digits – but on the centrist record he built as governor of Virginia. He left office earlier this year with high approval ratings from both Democrats and Republicans.

“The idea (is) that the way that Democrats win the White House is to nominate somebody who has won election in a red state,” said Jennifer Duffy, a political analyst at the nonpartisan Cook Political Report. “He had a very successful term. He had a lot to brag about.”

Warner dismissed speculation that his decision was based on any liabilities he would have had as a candidate.

“I can say with complete conviction, 15 months out from the first nominating process, I think I would have as good a shot as any of the potential candidates in the field,” he said in Richmond.

Instead, the 51-year-old Warner said that after four years of putting his personal life on hold as governor, he wanted to spend more time with his three teenage daughters.

“While politically this appears to be the right time for me to take the plunge, at this point, I want to have a real life,” Warner said.