Hillary Rodham Clinton, Barack Obama and John Edwards on Saturday joined three other Democrats who say they will skip states that break party rules by holding early primaries.

Their decision is a major boost to the primacy of four early voting states — Iowa, New Hampshire, Nevada and South Carolina — and a welcome development to the Democratic National Committee.

"We believe Iowa, New Hampshire, Nevada and South Carolina play a unique and special role in the nominating process," Clinton campaign manager Patti Solis Doyle said. "And we believe the DNC's rules and its calendar provide the necessary structure to respect and honor that role."

The DNC has tried to impose discipline on a handful of unruly states determined to vote before Feb. 5 and gain influence in the election cycle.

"Iowa, New Hampshire, Nevada and South Carolina need to be first because in these states ideas count, not just money," Edwards said. "This tried-and-true nominating system is the only way for voters to judge the field based on the quality of the candidate, not the depth of their war chest."

Obama said the DNC's nominating process is "in the best interests of our party and our nation."

Their pledges came a day after rivals Chris Dodd, Bill Richardson and Joe Biden endorsed the plan, which was promoted by Democratic leaders of the four states that have party approval to hold early contests.

They have now agreed that they won't compete in any other states that vote before Feb. 5, as Florida plans to do and Michigan is poised to do.

Their decision is a blow to Florida, which had moved its primary to Jan. 29, and Michigan, where the legislature this week voted to push its primary to Jan. 15. Michigan acted despite the DNC's threat to punish Florida by stripping it of its 210 delegates unless it comes up with another plan in the next four weeks.

The prospect of five candidates bypassing Florida and Michigan would essentially turn those contests into nonbinding beauty contests, with no delegates at stake if the DNC imposed its punishment.

Florida Democratic Party executive director Leonard Joseph said Saturday: "No matter which cards we're dealt, Florida Democrats are going to win the state's 27 electoral votes and elect a Democratic president in 2008. The country needs us."

The Florida party chairwoman, Karen Thurman, has criticized the pledge, calling it "a pact to ignore tens of millions of diverse Americans by a selfish, four-state alliance of party insiders."

Michigan Gov. Jennifer Granholm has encouraged candidates to ignore the pact, saying unfair trade policies and her state's manufacturing crisis were more important than the politics behind which states get to vote early. Granholm has been preparing to sign legislation that would move Michigan's contest to Jan. 15, despite the threat of DNC sanctions.

"We expect that all of the Democratic candidates for president will be on the ballot in Michigan on January 15th. We hope that every candidate will campaign here," Granholm said Saturday.

Among Republican presidential contenders, Michigan's decision to jump to Jan. 15 has been popular, said Saul Anuzis, the state's Republican Party chairman. Most of them plan to attend a GOP leadership conference there in September, he said.

Party rules for this cycle had Iowa's caucuses on Jan. 14, with tests in Nevada Jan. 19, New Hampshire Jan. 22 and South Carolina Jan. 29.

New Hampshire and Iowa are considering earlier contests to maintain their influence, but the pledge does not prohibit candidates from campaigning in those states even if they go earlier than the national party allows.

DNC rules committee member Martha Fuller Clark, co-chairwoman of Obama's New Hampshire campaign, applauded Obama's decision.

"The rules adopted by the DNC ensure that we recognize American diversity and, at the same time, the tremendous value of retail politics in selecting our next president," she said Saturday.

Dodd, Richardson and Biden have the most incentive to keep the contest focused on the states approved by the DNC. They have raised less money and can't afford to organize in multiple states at the same times, especially those with expensive media markets such as Florida and Michigan where Clinton is a substantial favorite in the polls.

Financial concerns also were a factor for Edwards, who has lagged behind Clinton and Obama in fundraising. Edwards also favored caucuses in Michigan, hoping a strong labor turnout would improve his chances, but the state had been moving toward a primary.