DES MOINES — They rolled the dice.
Whether it was because they were eager to leave behind the bitter divides of the last two decades or because they wanted to send a message that a small white state could transcend the issue of race, Iowa voters handed Senator Barack Obama a victory here Thursday and supported his improbable candidacy in defiance of those who warned he was too inexperienced in world affairs.
Instead, what seemed to drive them was the idea that Mr. Obama would present a new face for America in the world, with a coalition of Democrats and independents dispelling skepticism and flooding caucuses in all corners of the state to support a man who came to Washington only three years ago.
“We are one people,” Mr. Obama said. “And our time for change has come.”
It was only a year ago that Mr. Obama, 46, a first-term senator from Illinois, formally decided to seek the Democratic nomination, which even some of his closest advisers feared could diminish his long-term potential. As he learned to become a presidential candidate on the fly, seasoned political hands worked to build an organization here unlike any other, which ultimately helped to nearly double the turnout from the caucuses four years ago.
Mr. Obama praised Iowa voters for casting away a litany of concerns that his rivals had aired about his candidacy, like too little experience and questions of electability. But he conceded that his victory was only a beginning.
“This was the moment when we tore down barriers that have divided us for too long,” Mr. Obama said. “When we finally united people of all parties and ages.”
The strength of his performance — and a strong finish by former Senator John Edwards of North Carolina — shook the confidence of Senator Hillary Rodham Clinton’s campaign and created fresh uncertainty in the Democratic nominating contest. Even before Mr. Obama’s victory had been formally declared, the Clinton campaign announced that former President Bill Clinton would be dispatched to New Hampshire for a five-day blitz before the primary there on Tuesday. (It was Mr. Clinton who suggested that Mr. Obama’s candidacy would be a roll of the dice, a phrase that Mr. Obama turned into a mantra in recent days, often when appearing before overflowing crowds.)
“I congratulate Senator Obama and Senator Edwards,” Mrs. Clinton, of New York, said to supporters, with her husband and her daughter, Chelsea, behind her. “Together we have presented the case for change.”
With a confident smile, she added, “We’re going to get up tomorrow and keep pushing as hard as we can.”
After a yearlong campaign built upon a multimillion-dollar advertising campaign and a network of grass-roots organizers, Mr. Obama was supported Thursday evening by younger voters, voters looking for change, independents and very liberal Democrats. At the same time, he was the first choice of one-third of female voters.
In fact, the poll of Democrats as they entered the caucuses suggested that women were closely divided between Mr. Obama and Mrs. Clinton. Among men, Mr. Obama did better, according to the poll conducted by Edison/Mitofsky for the National Election Pool of television networks and The Associated Press.
While Mr. Obama’s candidacy gained steadily throughout the year, he also has capitalized on an unsteady electorate craving change. One of the largest applause lines he receives continues to be when he declares that President Bush will be out of office in only a year.
“The huge difference was that we had the greatest organization ever built in this state,” said David Axelrod, the chief strategist for Mr. Obama’s campaign. “And it was built on the backs of idealistic kids who came in here not just because they believed in Obama, but they wanted to change the course of history and the world.”
“One of the charges against Iowa is that we don’t really represent the rest of the country, and here’s a chance to make a statement about the inclusiveness of Iowa,” said Jon Muller, 42, who voiced his support for Mr. Obama at Precinct 73. “I’m just ready for a change, as opposed to a Clinton or Bush.”
At his caucus site at the Plymouth Congregational Church in Des Moines, supporters of Mr. Obama spilled out of the room, as they did in locations across the state.
The results of the Iowa caucuses, with Mr. Edwards and Mrs. Clinton in a narrow fight for second place, heightened the importance of the New Hampshire primary, where a trove of independent voters were already leaning toward Mr. Obama.
Mr. Edwards promised that his candidacy would continue. With his wife, Elizabeth, standing behind him, Mr. Edwards spoke to supporters at in Des Moines.
“The one thing that’s clear from this result here tonight is that the status quo lost and change won,” Mr. Edwards said.
Even though the Clinton advisers began lowering expectations for Mrs. Clinton’s performance weeks ago, saying that she had faced hardened, negative perceptions among Iowa voters that stemmed from her partisan and secretive image as first lady, the results raised new questions about her candidacy.
Indeed, in the closing days of the race here, some of her advisers began recalling that Mrs. Clinton’s deputy campaign manager recommended in May that she skip the caucuses altogether, after internal polling found that she had high negative ratings in the state.
She decided to compete here in spite of the fact that neither she nor her husband had deep political roots in the state.
Still, Mrs. Clinton’s supporters had expected her to win.
“I expected her to be first,” said Mario Gandelsonas, 68, an architect from New York who supports Mrs. Clinton and was in Des Moines on a work project. “But this is just the beginning. I know Hillary. She’ll be first, and she’ll beat them all in New Hampshire. This will give her incentive to fight even harder.”