DES MOINES, Iowa - Sen. Barack Obama swept to victory in the Iowa caucuses yesterday night, pushing Hillary Rodham Clinton to third place and taking a major stride in a historic bid to become the nation's first black president. Mike Huckabee rode a wave of support from evangelical Christians to win the opening round among Republicans in the 2008 campaign for the White House.

Obama, 46 and a first-term senator from Illinois, told a raucous victory rally his triumph showed that in "big cities and small towns, you came together to say, 'We are one nation, we are one people and our time for change has come.'"

Nearly complete returns showed the first-term lawmaker gaining 37 percent support from Iowa Democrats. Former Sen. John Edwards of North Carolina appeared headed for second place, relegating Clinton, the former first lady, to a close third.

As the results poured in last night from precincts across Iowa, it became increasingly evident that young voters, previously described as "elusive," "unreliable" and the "icing on the cake," played a crucial role in securing Obama's victory.

At two caucus precincts in northern Des Moines, held in adjoining auditoriums on Drake University's campus, Obama commanded the majority of caucus-goers, and was especially popular among the precincts young participants.

Peter Tomka, a senior at nearby Roosevelt High School, said he caucused for Obama primarily because of the Illinois senator's message of change.

"People have underestimated Obama up to now, but I think they're starting to see the things he can do for our country," Tomka said.

After first backing Democratic candidate Bill Richardson and then later supporting fellow Democrat John Edwards, Des Moines resident Sean Donovan said he ultimately joined the majority of Obama supporters at last night's caucus because he believes Obama can transcend the partisan divide and win over undecided voters in a general election setting.

"What (Obama) brings is the willingness to work with the other side, with Republicans or independents, much more so than any other (Democratic) candidate," Donovan said.

An hour east of the capital in Grinnell, home to the state's most delegate-rich precinct and home to progressive Grinnell College, Obama scored a convincing victory by earning 21 of the total 37 delegates in Grinnell's Ward One district.

Alec Schierenbeck, president of the College Democrats of Iowa, who caucused in Grinnell, said the turnout there among young people was "absolutely amazing." He said the majority of young caucus-goers in Grinnell - more than any other age group - caucused for Obama, which sends a message to the presidential race's other candidates about the power of young people in an election setting.

"(Obama) succeeded here in Grinnell because of their support," Schierenbeck said. "And what it proves is that when you take young people seriously, they will deliver."

Huckabee celebrated his own victory over Mitt Romney and a crowded Republican field.

"A new day is needed in American politics, just like a new day is needed in American government," the former Arkansas governor told cheering supporters. "It starts here, but it doesn't end here. It goes all the way through the other states and ends at 1600 Pennsylvania Avenue."

Huckabee, a preacher turned politician, handily defeated Romney despite being outspent by millions of dollars and deciding in the campaign's final days to scrap television commercials that would have assailed the former Massachusetts governor. He stressed his religion to the extent of airing a commercial that described himself as a "Christian leader" in his race against a man seeking to become the first Mormon president.

Nearly complete returns showed Huckabee with 34 percent support, compared with 25 percent for Romney. Former Sen. Fred Thompson and Sen. John McCain battled for third place, while Texas Rep. Ron Paul wound up fifth and former New York Mayor Rudy Giuliani sixth.

With the New Hampshire primary only five days distant, Clinton and Edwards vowed to fight on in the race for the Democratic nomination.

"We have always planned to run a national campaign," the former first lady told supporters at a noisy rally attended by her husband and their daughter, Chelsea. "I am so ready for the rest of this campaign, and I am so ready to lead."

Edwards, the Democrats' 2004 vice presidential nominee, told The Associated Press in an interview he would distinguish himself from Obama in New Hampshire by arguing that he is the candidate who can deliver the change that voters have shown they want.

"I'm going to fight for that change," he said by telephone from his hotel room in Iowa. "I've fought for it my entire life. I have a long history of fighting powerful interests and winning."

Not everyone was going on. Democratic Sen. Christopher Dodd of Connecticut announced he was leaving the race, and officials said Sen.