The only major candidate who has not served in Washington, Dean told the Democratic National Committee winter session that party leaders have not been tough enough on Mr. Bush nor committed to party principles. Rank-and-file Democrats, still stinging from GOP midterm victories in the fall, lined up afterward to shake his hand and offer their support.
"What I want to know is why in the world the Democratic Party leadership is supporting the president's unilateral attack on Iraq?" Dean said.
Speeches by Dean and three Democratic candidates underscored a split within the party over how strongly to criticize a popular Republican president, particular on an issue as volatile as war.
Donna Brazile, campaign manager for former Vice President Al Gore in 2000, said Dean tapped into the frustration of Democrats who felt their leaders pulled their punches in taking on Mr. Bush and Republicans in the fall campaign.
Barely clinging to her promise to remain neutral in the primary races, Brazile added, "Anybody who gets us off the floor and out of the fetal position, I'm for."
On Saturday, three candidates will address the DNC session that allows them to burnish their image with the party faithful while trying to rally dispirited Democrats.
Rep. Dick Gephardt of Missouri told the group, "We must disarm Saddam Hussein," and he said he was proud to sponsor a congressional resolution authorizing Mr. Bush to use force, if necessary.
"Shame!" a member of the audience shouted. Fellow DNC members nodded their heads in support and gave the protester a thumbs up.
A growing number of Democratic activists oppose war in Iraq or at least Mr. Bush's approach to handling Saddam, forcing the candidates to shift constantly and reassess their positions. Gephardt has said he supports Mr. Bush's get-tough policy on Iraq but not his diplomatic approach, the same position staked out by Sens. John Kerry of Massachusetts, Joe Lieberman of Connecticut and John Edwards of North Carolina.
Lieberman faulted the president for "weakening our alliances."
Former Illinois Sen. Carol Moseley Braun, a recent entry to the crowded Democratic field, said Saddam must be "driven out of business," but accused Mr. Bush of "saber-rattling that has made us all hostages to fear."
In an interview, Dean said that he opposes the congressional resolution and remains unconvinced that Saddam is an imminent threat to the United States. He said he would not support sending U.S. troops to Iraq unless the United Nations specifically approves the move and backs it with action of its own. "They have to send troops," he said.
Kerry's campaign manager, Jim Jordan, fired back, "Governor Dean, in effect, seems to be giving the U.N. veto power over national security decisions of the United States. That's an extraordinary proposition, one never endorsed by any U.S. president or serious candidate for the presidency."
Dean's campaign organized a demonstration of sign-toting supporters who also shook prescription bottles filled with loose change. It was a clattering ode to the candidacy of a doctor who says he has the prescription for change in America. Dean was an internist before he entered politics.
"If you want young people to vote in this country and if you want the 50 percent of adults over 30 to vote in this country that do not vote in today's election, then we had better stand for something, because that's why they're not voting," Dean said.
Immediately after the address, former Gore aide Brazile organized an impromptu meeting between her fellow black activists and Dean.
Ed Tinsley, a DNC member from Montana, was shaking his head in amazement after the Dean speech. "He got us riled up," Tinsley said. But Tinsley and several other Democrats cautioned that Dean's message carried just one day, and that there are many more to go against a field of experienced, well-financed candidates.