WASHINGTON - Howard Dean, once touted as the man most likely to succeed in the Democratic presidential race, folded his campaign yesterday after failing to win a single state.

"I am no longer a candidate," Dean told flag-waving supporters in his hometown of Burlington, Vt., where he returned after a weak third-place finish in the Wisconsin primary.

Dean said he would convert his campaign organization into a "grass-roots network" to change his party and the country.

He promised to support the Democratic ticket in the race against President Bush. But he also delivered a warning that hinted at prickly relations with the eventual nominee.

"Let me be clear. I will not run as an independent or a third-party candidate," Dean said. "But we will not be above ... letting our nominee know that we expect [him] to adhere to the standards that this organization has set for decency, honesty, integrity and standing up for ordinary American working people."

Dean's hoarse voice, and the cough that punctuated his speech, reflected the strains of the past month, when his chances of winning the nomination vaporized so fast that it was hard to believe they ever existed.

For much of the past six months Dean had appeared unstoppable. Many politicians had concluded that the former Vermont governor was on his way to the Democratic nomination. His party's 2000 presidential contenders, Al Gore and Bill Bradley, had endorsed him. Savvy Republicans, including Karl Rove, the top White House strategist, figured it would be a Bush-Dean race in the fall, as did many commentators.

Those expectations, which put Dean's face on magazine covers and national television, magnified his breathtaking fall. His collapse, so soon after his remarkable rise from obscurity, became a riveting spectacle.

In successfully linking his angry, insurgent message to the power of the Internet, Dean brought presidential politics into the Wired Age in a meaningful way for the first time.

By using online connections to build an army of small donors, he showed Democrats how to compete against deeper-pocketed Republicans in a post-soft money world. Along the way, he set a party fund-raising record. He also became the first Democrat to lose the nomination after out-raising his rivals in the year before the election.

Dean's emergence as a national figure was triggered by his full-throated challenge to the Washington establishment. He cast himself as the voice of the "Democratic wing of the Democratic Party" and quickly got the attention of insiders.

But it was his outspoken opposition to Bush's decision to take the country to war in Iraq - and his harsh criticism of rivals who voted for the war resolution, including Sens. John Kerry and John Edwards - that put Dean into the lead in the polls and the race for campaign cash.

A physician by training, he had started out to make universal health care the centerpiece of his campaign. "I had no idea this would happen," Dean told a reporter a year ago, after his antiwar stance had begun to create ripples among party activists strongly opposed to the war.

His anti-establishment image, and cultivated reputation for unvarnished talk, helped draw a legion of younger voters into politics. It also revived the activism of others from Dean's baby-boom generation, who had retreated to the civic sidelines.

That made his defeat at the hands of Kerry, a member of the party establishment, particularly hard to take. In recent weeks, Dean has not concealed his bitterness toward Washington, Democratic Party leaders and the national news media.

In his withdrawal speech, he sought to put his campaign's failure into the context of a wider social battle, noting the "enormous institutional resistance to change in this country." And he took unconcealed delight in telling supporters that his campaign had "literally terrified people, sitting in their salons in Georgetown, that they might actually have to look for work if we won."

Dean neglected to mention how, for months, he'd been recruiting a wide range of established Democratic experts in Washington as advisers. He also did not refer to his endorsement by establishment figures, such as Gore, whose backing served to blur his outsider image in the minds of Democratic voters.

According to some in his camp, the Dean campaign ultimately failed because of his inability to grow as a candidate. He was unable to make a successful shift from insurgent to front-runner, and in a way that would make voters comfortable with the idea of him as president. Instead, voters became increasingly focused on doubts about Dean's temperament. The role he carved out for himself as the voice of angry Democrats prevented him from convincing voters that he had the steadiness to lead the country in the new age of terror.

In interviews, Dean advisers traced the start of his downfall to last fall, days before he secured the endorsement of two powerful labor unions, in retrospect the high point of his campaign. Yesterday, Dean thanked the labor leaders who stuck with him, "when others abandoned us," a reference to AFSCME, the public employees union that deserted him this month once his campaign began to fail.