Republican presidential hopefuls crisscrossed Iowa Saturday as they made a final frenzied push for votes ahead of the heartland state's first-in-the-nation contest to pick the party's nominee.

Former Massachusetts governor Mitt Romney, savoring his regained frontrunner status, ripped President Barack Obama's annual vacation to his native state of Hawaii as a sign the Democrat was out of touch with struggling Americans.

"He's in Hawaii right now. We're out in the cold and the rain and the wind because we care about America, he's out there. He just finished his 90th round of golf," he told a rowdy crowd in West Des Moines Friday.

Former senator Rick Santorum credited his relentless crisscrossing of the state and his fierce, take-no-prisoners appeals to social conservatives for his surge to third place in the polls ahead of Iowa's caucuses on Tuesday.

"The consistent, strong, conservative message, full throttle, not apologizing, and with a track record of being able to win tough elections -- I think that's finally starting to resonate," he said in an Ames, Iowa bar crowded with Iowa State university football fans cheering the team's televised exploits.

Former House speaker Newt Gingrich stunned a packed audience in a coffee shop here by choking back tears as he recalled his late mother's illness and death in a rare display of gentle emotion from the erstwhile back-bench bomb-thrower.

"I get teary-eyed every time we sing Christmas carols. My mother sang in the choir," said Gingrich, whose once strong standing in Iowa has crumbled under a ceaseless barrage of attack ads from rivals looking to tear him down.

And Representative Ron Paul of Texas, running neck and neck to Romney in Iowa, defended the anti-government views and full-throated denunciations of overseas US military action that other candidates have condemned as "dangerous."

"It sort of baffles me a whole lot because I think big government is dangerous," Paul said, according to local radio. "I think wars fought endlessly is dangerous. I think printing money and (expanding) government at will -- that is what is dangerous."

Texas Governor Rick Perry and Representative Michele Bachmann also stumped in Iowa, while former US China envoy Jon Huntsman wooed voters in New Hampshire, which holds its nominating primary on January 10.

While Romney and Paul have built up the most impressive machines, and Santorum aims to harness his new momentum, the caucus results could still swing wildly because an estimated four in ten Iowans are still making up their minds.

Unpredictable 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.

But a victory here can lift a sagging campaign or give a top contender an extra air of inevitability, bringing fundraising dollars, endorsements and voter support that can shape the rest of the state-by-state nominating battle.

So on New Year's Eve, the top candidates were scheduled to hold 11 events throughout the state, in places like a public library in Indianola, the Gigglin' Goat restaurant in Boone, or the National Sprint Car Museum in Knoxville.

On the Democratic side, which lacked for suspense because Obama is unopposed, party faithful were eagerly awaiting a live message from the president to be beamed into caucus sites.

Obama, currently taking his annual Christmas and New Year vacation with his family in his native state of Hawaii, faces an uphill fight for re-election, weighed down by the sour economy and historically high unemployment.

Romney, who hopes to take on the president in the November 2012 elections, pointed out a sign at the rally that read "In Obama We Trusted, Now Our Economy Is Busted" and declared: "You got it right, brother."

Romney has the backing of much of the Republican establishment -- yet he has not been able to swell his support above 30 percent of Republican voters, and faces stubborn doubts about his conservative credentials.

Undecided Maura Kenworthy, 35, told AFP at the rally that she voted for Obama in 2008 and felt sympathy for the embattled president -- "I don't envy his job" -- but will not support him next year "unless something drastically changes."

At Santorum's bar room appearance, Iraq war veteran Rick Rodgers described himself as "all in" for the former senator because after a face-to-face discussion "I felt I could trust him."