DES MOINES, Iowa — Democrats Barack Obama, Hillary Rodham Clinton and John Edwards fought for first Thursday in Iowa's presidential caucuses, a multimillion-dollar exercise in grass-roots democracy and the initial, critical test in the campaign for the party's 2008 nomination. Mitt Romney and Mike Huckabee vied for the Republican victory.

Iowans rendered their judgments in meetings at 1,781 precincts from Adel to Zingle, in schools, firehouses and community centers where the candidates themselves could not follow.

Earlier, the contestants had their final say.

Huckabee told a crowd in Burlington, "It's about believing in a cause," a summation that rivals in both parties could easily embrace. Likewise Edwards' plea to his backers in Iowa City: "This thing could be really close. ... We need you to make calls, talk to your friends." And Obama in Des Moines, when asked how he was feeling: "I feel great, although my throat. ..."

Win or lose, there was little time for rest. New Hampshire's first-in-the nation primary is set for next Tuesday, and the campaign quickly accelerates into a rush of contests culminating in more than two dozen on Feb. 5.

With President Bush constitutionally barred from seeking re-election, both parties had wide-open, costly campaigns.

Obama, a first-term Illinois senator, stressed a need for change as he campaigned to become the first black president in history. Clinton, a New York senator, boasted of her experience as she worked to follow her husband into the White House and become the first woman to occupy the Oval Office. Edwards, his party's 2004 vice presidential candidate, cast himself as the implacable enemy of special interests as he aimed to improve on last time's second-place showing in the state.

New Mexico Gov. Bill Richardson, Sens. Chris Dodd of Connecticut and Joe Biden of Delaware and Rep. Dennis Kucinich of Ohio also contested the state.

Romney, a former Massachusetts governor, stressed his background as a businessman and organizer of the 2002 Olympics, and he worked to persuade conservatives to ignore his earlier positions on abortion and gay rights. He ran the only commercials of the campaign critical of a rival, hitting Huckabee for his positions on immigration and the pardons he issued while governor of Arkansas.

Huckabee, an ordained Baptist minister, pinned his hopes on evangelical conservatives who accounted for 40 percent of caucus-goers or more. By his account, he risked his candidacy when he decided not to air commercials criticizing Romney in return.