DES MOINES, Iowa – Mitt Romney's quest to swiftly lock down the Republican presidential nomination with a commanding finish in the Iowa caucuses was spoiled Tuesday night by the surging candidacy of Rick Santorum, who fought him to a draw on a shoestring budget by winning over conservatives who remain skeptical of Romney.

In the first Republican contest of the season, the two candidates were separated by only a sliver of votes. The outcome offered Santorum a chance to emerge as the alternative to Romney as the race moves to New Hampshire and South Carolina without Gov. Rick Perry, who announced he was returning to Texas to assess his candidacy.

"Being here in Iowa has made me a better candidate," Santorum said, arriving at a caucus in Clive, where he urged Republicans to vote their conscience. "Don't sell America short. Don't put someone out there from Iowa who isn't capable of doing what America needs done."

The Iowa caucuses did not deliver a clean answer to what type of candidate Republicans intend to rally behind to try to defeat President Barack Obama and win the White House. With 99 percent of the vote counted, Santorum and Romney, whose views represent widely divergent party factions, each had 24.6 percent.

The last time the Iowa caucuses produced such a close outcome was in 1980, when George H.W. Bush beat Ronald Reagan by 2 percentage points.

Rep. Ron Paul of Texas finished a close third on Tuesday with 21 percent of the caucus votes. "We will go on," he said in an upbeat speech. "There is nothing to be ashamed of."

The Iowa caucuses, which sounded the opening bell of the Republican contest, did not bring the clarity to the nominating fight that Romney had hoped. But even though he did not secure the commanding victory he had fought for in the last week, he handily dispatched two rivals who were once seen as his biggest threats, Perry and former House Speaker Newt Gingrich.

Gingrich was in fourth place with 13.3 percent of the votes, followed by Perry with 10 percent and Rep. Michele Bachmann of Minnesota with 5 percent. They pledged to press on, but it remained an open question whether all of the candidates would be on the stage for the next debate Saturday in New Hampshire.

"There will be a great debate in the Republican Party before we are prepared to have a great debate with Barack Obama," Gingrich said, pledging to raise the intensity of his criticism of Romney before the next contests. He offered a glimpse at his approach, calling Romney a liar whose conservative credentials could not be trusted.

The determined band of Republicans caucusgoers – divided on the candidates but united in their desire to defeat Obama – streamed into firehouses, gymnasiums and even a few living rooms across Iowa for the precinct meetings. The caucuses do not award any of the 1,150 delegates needed to win the party's nomination, but the result began reshaping the race.

A snapshot of the Republican mind-set, according to polls of voters as they entered caucus sites, found that Romney had won the most support among those who said the ability to defeat Obama was the most important quality in a candidate.

Romney's business experience, which is the spine of his candidacy, was a draw for voters concerned about the economy. Among voters who said the economy was the issue that mattered most in deciding whom to support, a plurality – about a third – said they would support Romney.

In one of the most conservative pockets in the state, the northwestern Iowa town of Alton, a supporter of Romney urged Republicans gathered at a firehouse to resist "throwing your vote away."

"I didn't vote for Mitt Romney in the last caucus, and I wish things had turned out differently," said Dan Ruppert, who rose to deliver a testimonial for Romney. "I'm definitely going to vote for Mitt Romney now."

The surveys found that Paul had far outpaced his rivals among caucusgoers under 40. But he dropped behind Romney and Santorum among voters 40 and older. Even though older caucusgoers made up a larger portion of the electorate, Paul's outsized lead among younger voters kept him competitive.

In the survey of voters arriving at caucuses, which was conducted by Edison Research for the National Election Pool of TV networks and the Associated Press, nearly 4 in 10 said they had never attended a caucus before. Those new attendees supported Paul over any other candidate.

Many caucusgoers did not make up their minds until late; entrance polls indicated nearly half had decided whom to support within the last few days. Santorum was the candidate who benefited the most from these late deciders – a third of them backed him.

Nearly 6 in 10 voters consider themselves evangelical or born-again Christians, the poll found, which illustrated the surge for Santorum in the closing days of the campaign.

Santorum now faces a challenge of trying to broaden his campaign organization on the fly to compete with the structure that Romney has spent years building. His aides said he will campaign this week in New Hampshire and South Carolina, vowing to compete with Romney everywhere.

As Republicans turned out across the state to render the first judgment of the candidates, some voters conceded that they were still wrestling with selecting someone who stands the best chance of winning in November or one who is fully aligned with conservative principles.

Don Lutz, who works in real estate, arrived early and called himself a "Newt guy." But he said he would not cast his vote that way. He said he was supporting Romney.

"I don't want to have a vote for nothing," Lutz said in an interview at his caucus meeting in Clive, a suburb of Des Moines. "I just don't think that Newt is going to be there in the end. When I look at the business side of things, Mitt is probably the most qualified."

While Republicans were the focus of the night, thousands of Democrats gathered at their caucus meetings, too. Obama addressed supporters via video, urging them to come to his defense in the general election.

"It's going to be a big battle, though," Obama said. "I hope you guys are geared up."

A woman piped in from Cedar Rapids: "How do you respond to people who say you haven't done enough?"

"That's why we need four more years," Obama said.

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