DES MOINES, Iowa — Sen. Barack Obama of Illinois, a first-term Democratic senator trying to become the nation's first African-American president, rolled to victory in the Iowa caucuses on Thursday night, lifted by what appeared to be a record turnout of voters who rejected the criticism that he did not have enough experience.

"They said this day would never come. They said our sights were set too high. ... But on this January night, on this defining moment in history, you have done what the cynics said we couldn't do. You did what the state of New Hampshire can do in five days," Obama said.

Obama's victory amounted to a significant setback for Sen. Hillary Rodham Clinton of New York, who just months ago appeared to be the front-runner for the Democratic presidential nomination but has watched her position erode over the past several months. The result also left uncertain the prospects for John Edwards, a former senator from North Carolina, who had staked his second bid for the White House on winning this state.

Candidates Sen. Joe Biden, D-Del., and Sen. Chris Dodd, D-Conn., announced they are dropping out of the race due to their poor showing in Iowa.

On the Republican side, Mike Huckabee, the former governor of Arkansas who was barely a blip on the national scene just two months ago, defeated Mitt Romney, a former Massachusetts governor, delivering a serious setback to Romney's high-spending campaign and putting pressure on Romney to win in New Hampshire next Tuesday.

Huckabee won with 34 percent of the vote, after 65 percent of precincts had reported. Romney had 24.9 percent, former Sen. Fred Thompson of Tennessee had 13.7 percent and Sen. John McCain of Arizona had 13.2 percent.

On the Democratic side, with 80 percent of precincts reporting, Obama had 36.3 percent, Edwards 30.5 percent and Clinton had 30.2 percent. Gov. Bill Richardson of New Mexico was fourth, at 1.9 percent.

A record number of Democrats turned out to caucus, producing scenes of overcrowded firehouses and schools and long lines of people waiting to sign in. Obama's victory in this overwhelmingly white state stood as a powerful answer to the question of whether America was prepared to vote for a black person for president. At the same time, the apparent surge of independent voters to his side, as suggested by polls of voters entering the caucuses, suggested his potential appeal in a general election.

The result sent waves of apprehension across Clinton's camp, and she turned her attention to New Hampshire. Aides said that former President Bill Clinton would go there immediately and spend the next five days campaigning in a state where he has always been strong.

On the Republican side, Romney had blanketed the state with television advertisements and, with a nod to the way campaigns are normally won here, built an extensive get-out-the-vote operation that carted Romney's supporters to the polls all days. As polls showed Huckabee rising, Romney responded with a month-long barrage of ads attacking him on immigration and taxes.