With time running out, rivals of surging Republican Rick Santorum raised doubts about his conservative record on Monday in hopes of heading off a last-minute victory by the former senator a day before Iowa kicks off the 2012 presidential election season.

Santorum, a second-tier candidate until a jump in the polls last week, claimed the momentum as he and the other Republican candidates barnstormed across Iowa making final arguments and trying to bolster turnout ahead of Tuesday's Iowa caucuses.

Former Massachusetts Governor Mitt Romney and libertarian congressman Ron Paul are neck-and-neck in the lead in Iowa polls in the start of the fight to decide who will face Democratic President Barack Obama in next November's election.

But Santorum, uniting voters on the Christian right who have been divided for months, could pull off a surprise. The top three or four finishers will likely have momentum, and maybe more money, to go into next week's New Hampshire primary.

Santorum's 11th-hour charge is just the latest twist in the Republican Party's tortuous road to reclaim the White House - a race that has changed front-runners half a dozen times already. In a time of weak economic and job growth and bitter bipartisan fights in Washington, voters seem to be unsure of their choices.

Iowa is no different. A poll by the Des Moines Register said 41 percent of those who will participate in the Iowa caucuses on Tuesday are undecided.

This is as wide open as we've ever seen it and the caucuses are just 24 hours away, said Tim Albrecht, spokesman for Republican Governor Terry Branstad.

RICK VS RICK

Texas Governor Rick Perry, who could suffer with a good Santorum showing, tried to slow the momentum of the former Pennsylvania senator, who lost his re-election bid in 2006.

Perry told MSNBC that Santorum's conservative credentials are in doubt because he backed costly government spending projects and supported the re-election of moderate Pennsylvania Republican Senator Arlen Specter, who voted for bank bailouts that conservatives disliked.

Paul took aim at Santorum's conservative record, too, telling CNN: He's very liberal ... He spends too much money.

Santorum, who reported a spike in fundraising, is peaking at the best possible moment, emerging from the pack as a conservative alternative to Romney after Perry, Newt Gingrich and Michele Bachmann have faltered. Iowa Republican strategists were not convinced he would claim victory, thinking instead he might finish second.

Santorum, forced to defend himself, waved off the criticism in Polk City, Iowa.

I am actually proud of my record. It is not unblemished. But if you look at my record on spending you are seeing someone who is a big supporter of a balanced budget amendment, he said.

Iowa voters had a choice to make - choose who they think is the strongest conservative, or pick who they think will be the most electable against Obama.

Undecided voter Patrick Brehm, attending a Romney rally in Dubuque, explained the difficulty in making a decision: Bachmann's campaign has run out of steam, America won't stand for Paul and Gingrich lacks integrity.

He said he likes Romney but doubts he could withstand the screaming and gnashing of teeth that will come with budget cutting.

Santorum is probably the most viable. I tend to think he could probably take the heat, Brehm said.

Paul, who has risen in popularity due to his anti-war positions, said in Des Moines that money was flowing into his campaign and that enthusiasm was greater than during his 2008 presidential bid.

The American people are stirring, Paul said. This is what this campaign has been all about. We are sick and tired of the expansion of government. Tomorrow is a very important day. You carry a lot of weight in this state. Send a message.

'MOMENTUM ... AROUND MITT'

Romney, who is more moderate and has establishment backing, looked to have a good day on Tuesday under most scenarios. He has spent far less time in Iowa than his rivals yet stands a chance to win the caucuses and go to his home turf of New Hampshire with a big head of steam.

Team Romney would love to pull off a surprising victory in Iowa but would consider a Paul or Santorum win good for Romney, since Romney aides consider Gingrich and Perry to be more dangerous rivals in the long run.

A couple hundred people turned out at a fairgrounds in Davenport, Iowa, for a Romney rally as howling winds chilled the Midwestern state.

Romney's wife, Ann, told the crowd that Iowans appear to increasingly believe her husband will win the nomination.

I sense a feeling, a coalescing, a momentum or whatever you want to call it around Mitt, she said. I think people are starting to figure out that this is the guy that is going to beat Barack Obama.

Gingrich tried to puncture the image of Romney as the more electable Republican. He tumbled out of the front-runner spot down to fourth place in a Des Moines Register poll after weeks of blistering attacks from Romney and others.

People who describe him as the front-runner have to ask yourself the question, if you spent that many million dollars to get to 23 percent, how can he possibly think he's the most electable candidate? he told reporters.

While the Republicans dominate the airwaves, Democrats tried to get their message across to Americans tuning in to Elections 2012. All the candidates, the Democrats said, are far to the right of most Americans.

The Republicans have allowed the Tea Party extremists to hijack their party, said Democratic National Committee Chairwoman Debbie Wasserman Schultz.