Mitt Romney Wednesday won the first battle in the 2012 White House race, taking Iowa by a razor-thin margin to defeat Christian conservative Rick Santorum by just eight votes.

The former Massachusetts governor won 30,015 votes in Tuesday's Republican nominating contest over 30,007 for Santorum, Iowa officials announced after the two men slugged it out to a nail-biting photo-finish.

"Congratulations to governor Mitt Romney, winner of the 2012 Iowa caucuses.

Congratulations to senator Santorum for a very close second place finish, an excellent race here," Iowa Republican Party chairman Matt Strawn said.

It marked a remarkable comeback for Santorum in the battle to capture the Republican Party crown and challenge President Barack Obama on November 6.

"You have taken the first step in taking back this country," Santorum, who surged here after being given up as politically dead weeks ago, told cheering supporters at what was essentially a victory rally after the Iowa caucus.

The former senator, a devout Catholic who opposes abortion and contraception and has a hawkish foreign policy, took a shot at what are seen as Romney's more centrist views, saying "what wins in America are bold ideas, sharp contrasts."

Romney, a former Massachusetts governor and millionaire venture capitalist, said he and Santorum each had "a great victory" and congratulated Representative Ron Paul on his third-place finish -- then trained his guns on Obama.

"This has been a failed presidency," Romney said late Tuesday, in a variation of the stump speech he used in Iowa, calling Obama "in over his head"

and vowing "I will go to work to get America back to work."

Romney and Santorum ended with 25 percent each, Paul stood at 21 percent, and former House speaker Newt Gingrich led the second tier of candidates with about 13 percent of the vote.

"This movement is going to continue and we're going to keep scoring just as we have tonight," said Paul, 76, a small-government champion who has stumped heavily in his opposition to foreign aid and military interventions overseas.

Gingrich, whose support in Iowa crumbled under a barrage of attack ads chiefly run by Romney's allies, served notice he would show no mercy as the battle for the party's nomination shifted to New Hampshire's January 10 primary.

After a months-long campaign onslaught -- barrages of television attack ads, telephone calls and mailings, candidates blitzing across the state -- Iowans headed into hundreds of caucus sites around the mostly rural heartland state.

They gathered Tuesday in places like school gymnasiums, libraries and church basements to speak out in front of neighbors on behalf of their chosen candidate and then vote by secret ballot.

The Iowa caucuses came against the backdrop of a sour, job-hungry US economy that weighs heavily on the embattled Obama's bid for a second term, four years after he promised "hope and change" in his historic 2008 victory.

The president, in a message beamed to Democrats holding their own caucuses across this mostly rural state, pleaded with them to stick with him, saying:

"Change is never easy."

"We've been making steady progress as long as we can sustain it. And that's what this is going to be all about," he said.

The quirky process is likely to set the tone for the rest of the state-by-state battle, lift or bury a sagging campaign, and add luster to a shining presidential prospect.

Texas Governor Rick Perry announced he would return to his home state to decide whether to keep running, while Representative Michele Bachmann vowed to fight on despite her woeful sixth place finish.

Romney had made little secret that he hoped a strong showing in Iowa, a romp in New Hampshire, and another success in South Carolina, would let him lock up the nomination months before the general election.

He still may: Paul's unorthodox libertarian views have earned him a devout following, but he is seen as uncompetitive in other states, while Santorum, 53, faces an uphill fight to match Romney's massive national organization.

Still, while Romney's vast campaign warchest and high-profile endorsements have fed his image as the candidate to beat, he faces stubborn doubts about his conservative credentials, as well as his Mormon faith, and has been unable to increase his support among Republican voters nationwide above 30 percent.

Iowa -- where unemployment is well below the national average -- is also an unreliable predictor of presidential fortunes: Senator John McCain, the eventual nominee in 2008, came in fourth that year. (AFP)