"The fight that we began can and must continue," Dean said in a statement posted on his campaign Web site. "Although my candidacy for president may end today, the most important goal remains defeating George W. Bush in November, and I hope that you will join me in doing everything we can to support the Democrats this fall."

Dean said the new initiative would be launched in the coming weeks but did not offer details.

"The truth is: change is tough. There is enormous institutional pressure in our country against change. There is enormous institutional pressure in Washington against change, in the Democratic Party against change. Yet, you have already started to change the party and together we have transformed this race," Dean said. "The fight that we began can and must continue."

Dean, who went winless in 17 caucuses and primaries after falling from leading contender early in the year, does not intend to endorse either John Kerry or John Edwards, a campaign aide told The Associated Press on condition of anonymity. Dean has been impressed with Edwards and suggested on the campaign trail that he would make a better nominee, but Dean has decided to stay out of the Kerry-Edwards contest, the aide said.

Dean was planning to call both men before publicly announcing his withdrawal from the race this afternoon.

Dean exits the active race certain in the knowledge that he will live on in the annals of U.S. politics for shattering Democratic fund-raising records with $41 million collected in a single year — as well as on late-night television and Internet parodies for a high-octane concession speech on the night of the Iowa caucuses that he’s likely never to live down.

The former Vermont governor is the political equivalent of a supernova. Once a long-shot candidate, the Internet phenomenon filled his campaign coffers and attracted thousands of supporters through the spring and summer, pushing him to the head of the crowded Democratic field.

The leader in national polls — and more important state polls in the first states of Iowa and New Hampshire — Dean seemed poised to win the nomination in a runaway. In the end, he never won a single state through 17 contests.

Historians will judge, but Dean and his devoted supporters are convinced that they more than anyone else defined the Democratic debate through his unwavering criticism of President Bush, the Iraq war and Democrats who helped Bush push his agenda through Congress.

"Because of your work, we have already written the Democratic Party platform," Dean declared Monday night at an exuberant Madison rally that harkened to the heady days when he was more focused on a running mate than exiting the race.

For that latter part of 2003 and the early days of this year, Dean seemed untouchable, emerging from miscues and gaffes with yet another fund-raising record or high-profile endorsement.

Nothing could dissuade the 640,000 people who joined his campaign via his Web site. They contributed $41 million last year and then pumped millions more this year into a campaign that was faltering even before Iowans dealt the first blow.

Dean was the most unlikely of heroes for this movement of liberals, disaffected voters and youth. Born to wealth on New York’s Park Avenue, his Yale pedigree was much closer to Bush’s than the working people to whom he said he was giving voice.

As he left the Vermont governor’s office in January 2003 after nearly 12 years, Dean had a presidential campaign staff of a half-dozen and about $157,000 in the bank.

But one of those staffers had found a then-obscure Internet organizing site, known as MeetUp.com. Dean became the first political candidate to sign up for it and suddenly thousands of people were finding him, organizing local events and fund-raisers and slowly making him a force.

His blunt speaking style and full-throated opposition to the Iraq war at a time when almost all of the other major contenders were trying to explain their support for it gave him an edge.

Even then he was still little more than an afterthought, but he had raised enough money to begin competing and was relentless in appearing everywhere he could. By February last year, he had begun focusing his criticism not just on Bush but on his fellow Democrats, accusing them of being too timid in fighting for the party’s core principles.

"I’m Howard Dean and I represent the Democratic wing of the Democratic Party," Dean declared at a Democratic National Committee meeting in Washington last year that caught everyone’s attention. The line had been a staple of the late Minnesota Sen. Paul Wellstone.

Dean tapped into Democrats’ nagging belief that their national leaders had lost their way and were too blindly allowing Bush and the Republicans to set the agenda.

But even at that early stage there were signs of Dean’s penchant for speaking before all the facts were straight. He apologized to rival John Edwards for mischaracterizing the North Carolina senator’s position on the Iraq war, and offered his regrets to foe Bob Graham for dismissing him as a second-tier candidate.

Each misstep, though, seemed only to embolden Dean and his supporters.

After Dean’s performance on NBC’s "Meet the Press" last June was widely panned, supporters decided to prove the establishment wrong, raising more than $3 million over the Internet in just a week.

Suddenly, Dean appeared to be the man to beat. The "People-Powered Howard" movement had begun and the money kept rolling in.

It got his opponents’ attention, too, and they stepped up the criticism. Dean stirred controversy in November for saying he wanted "to be the candidate for guys with Confederate flags in their pickup trucks," then quieted the uproar by winning the endorsement of two of the country’s largest unions — the American Federation of State, County and Municipal Employees and the Service Employees International Union.

Dean then snagged one of the biggest prizes — the backing of former Vice President Al Gore, the nominee in 2000.

Days before the Iowa caucuses, four-year-old tapes surfaced of Dean telling Canadian television that caucuses are dominated by special interests. He doused that firestorm quickly by winning the endorsement of Iowa Sen. Tom Harkin.

While it always appeared that Dean could emerge unscathed from the missteps, ultimately, it added up and voters decided to go with a familiar Washington face.