Barack Obama and John Edwards on Saturday joined three other Democratic presidential contenders planning to skip states that break party rules by holding early primaries. Their pledge leaves front-runner Hillary Rodham Clinton alone in planning to compete in Florida and Michigan.

Obama's and Edwards' pledge came a day after Sen. Chris Dodd of Connecticut, New Mexico Gov. Bill Richardson and Sen. Joe Biden of Delaware said they would not campaign in such states.

"As I have campaigned across America over the last six months, it's become clear that Governor Dean and the Democratic National Committee have put together a presidential nomination process that's in the best interests of our party and our nation," Obama, the Illinois senator, said in a written statement.

The five have signed onto a pledge circulated by Democratic leaders of the four states that have party approval to hold early contests — Iowa, Nevada, New Hampshire and South Carolina. The pledge says they will not compete in any other states that vote before Feb. 5, as Florida plans to do and Michigan is poised to do.

"Iowa, New Hampshire, Nevada, and South Carolina need to be first because in these states ideas count, not just money," Edwards, a former North Carolina senator, said in a written statement. "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."

The chairwoman of the Florida Democratic Party, 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."

Clinton aides had said they were reviewing the pledge.

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. The caucuses and primaries are to select delegates for the party's national nominating convention in the summer.

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.

Florida has scheduled its primary for Jan. 29, and will not have any delegates seated at next year's Democratic National Convention unless they change their plan in the next four weeks by order of the party.

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

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 cannot 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.