(Reuters) - Republican White House hopefuls launched a two-day dash to the finish in Iowa Sunday, with front-runner Mitt Romney poised for a strong showing that could set him on the path to the nomination.

Romney holds a slight edge over rival Ron Paul in recent polls in Iowa's first contest in the state-by-state battle to pick a challenger to President Barack Obama in 2012.

I'm pretty confident we'll have a good night. I don't know who's going to win, Romney told supporters at a packed restaurant in Atlantic, Iowa, adding he was energized ahead of Tuesday's contest.

Even a strong second-place showing in Iowa would be good news for the former Massachusetts governor. Paul could have trouble competing with him in later contests in New Hampshire, where Romney leads in polls, and in other states.

Romney, who spent millions in Iowa in 2008 only to lose, did not campaign hard in the state until the last week.

He picked up the endorsement on Sunday of the Quad-City Times, which praised his business background as a former head of a private equity firm and said he had the best chance of beating Obama.

We do not want to see the president face a token challenge in 2012, the newspaper said. Romney presents a far more serious challenge than any other caucus contender.

Rick Santorum, a former Pennsylvania senator, has surged past former House Speaker Newt Gingrich into third place in polls, building momentum in the final days of a close race that has seen a series of candidates rise and fall.

He urged supporters at a coffee shop in Sioux City to send a shock wave across the country by giving him an upset win.

Lead this country. That's what I ask the people of Iowa. Lead, don't defer, Santorum said. Don't put forward somebody who isn't good enough to do what is necessary to change this country.

Minnesota Rep. Michele Bachmann, who could face the end of the line if she does badly in Iowa, went to church to woo the critical Christian conservative vote, which has been split between her, Santorum, Gingrich and Rick Perry.

Bachmann has sunk to the bottom of polls and is beset by a lack of money and staff desertions.

On this Jan. 1, 2012, I admonish you, don't for one moment think that your adversity is one that cannot be scaled, Bachmann told churchgoers at a service in Oskaloosa, making biblical references to underdog Israelites defeating their enemies.

'A LOT LIKE BUSH'

Texas Gov. Rick Perry said on Fox News Sunday he was not focused on winning evangelicals, although he has aired several television ads aimed directly at gaining their support.

Romney, who attended a Mormon church service in Iowa on Sunday morning, likely raised more than $20 million in the final three months of 2011, a Republican source said.

That amount would almost certainly put him far in front of his Republican rivals and underscores the long-term advantage he has in organization and money.

We're looking better this quarter than any other quarter so far, Romney said, although he did not give a final number. He raised $14 million in the third quarter.

A win in Iowa for Romney, combined with a victory in his stronghold of New Hampshire on Jan. 10, could put him on a path to clinch the nomination early. It would make him the first Republican who is not an incumbent president to win the party's first two contests.

Obama's campaign has already begun attacking Romney, who has taken the president to task on his handling of the economy.

Romney is distrusted by some conservatives who remember his past support for abortion rights and for a state healthcare plan similar to Obama's federal overhaul.

Romney just has to prove that he's conservative enough for me, said Eleanor Stump, a 70-year-old Tea Party member from Sheldon, Iowa. I don't like the way he's flip-flopped.

Stump said she had initially supported Herman Cain, who dropped out of the race after charges of an extramarital affair, then went to Perry, then back to Cain and then to Gingrich. I've gone back and forth so many times, she said.

Gingrich, the former House speaker who has dropped in Iowa polls after an onslaught of attack ads from Paul and a group that backs Romney, said he would take a more aggressive tone in fighting back.

Governor Romney remains basically a Massachusetts moderate, and he has not ... broken out, despite spending millions of dollars, he said, adding he would start a discussion of the state healthcare plan Romney backed, called Romneycare by critics.

New Hampshire was the perfect state to have a debate over Romneycare, and to have a debate about tax paid abortions, which he signed, and to have a debate about putting Planned Parenthood on a government board, which he signed, and to have a debate about appointing liberal judges, which he did, he said.

A Des Moines Register poll on Saturday said 41 percent of Iowa Republicans were still capable of changing their minds by Tuesday when they kick off the 2012 presidential election cycle ahead of the November 6 election.

The newspaper poll, conducted Tuesday through Friday, showed Romney with 24 percent support and Paul with 22 percent, within the margin of error of 4 percentage points and similar to other polls showing the two battling for the top spot in Iowa.

Santorum had 15 percent support and Gingrich 12 percent. In fifth place was Perry with 11 percent, and Bachmann, a U.S. representative, was sixth with 7 percent.

Paul, who did not campaign in Iowa on Sunday but will return on Monday, shrugged off charges he could not beat Obama and that his non-interventionist views on foreign policy and newsletters published under his name in the 1990s that featured racial remarks put him out of the mainstream.

I would say that I'm pretty mainstream. I think that people who are attacking me now are the ones who can't defend their records, and they've been all over the place, Paul, a longtime representative from Texas, said on CNN's State of the Union.

(Additional reporting by Bill Trott, Eric Johnson in Iowa; Editing by Alistair Bell and Stacey Joyce)