MANCHESTER, New Hampshire (Reuters) - With Mitt Romney poised to stride toward the Republican presidential nomination by capturing New Hampshire on Tuesday, all eyes were on whether he could win big enough to convince his party he is the best candidate to defeat Democrat Barack Obama.
Despite rivals' fierce 11th-hour attacks painting him as a heartless corporate raider who enjoys cutting jobs, the former governor of neighboring Massachusetts carried a sizeable poll lead into primary day.
Rivals Ron Paul, who appeals to New Hampshire's libertarian strain, and more moderate Jon Huntsman were in a battle for runner-up in the small New England state known for bucking expectations.
A millionaire former businessman who says his private sector experience will help galvanize America's economy, Romney's bigger challenge might be at the next primary in South Carolina, where conservatives are traditionally strong.
Romney would be the first Republican who is not an incumbent president to win the first two early voting states, after his slim eight-vote victory over former Pennsylvania Senator Rick Santorum a week ago in the Iowa caucuses
But Romney has failed to excite the Republican base and was looking to go beyond the lukewarm endorsement of voters like Dave Searles, 56, a Windham software developer. He said he cast his ballot for Romney mainly because he was most likely to beat Obama.
"He wouldn't have been my first choice, but sometimes you have to make sacrifices," he said.
Santorum, a socially conservative former senator, has trailed in New Hampshire polls despite coming in just behind Romney in Iowa. Newt Gingrich, a former speaker of the House of Representatives, is also well behind.
Romney visited a polling station in Manchester and said he hoped the state would make a "big statement" for his candidacy. "You see great enthusiasm," he said.
A resounding win in New Hampshire would provide momentum going into South Carolina on January 21 and Florida on January 31. Romney leads in polls of both states and victories there would all but sew up his nomination to face Obama as he seeks re-election on November 6.
A Reuters/Ipsos poll on Tuesday showed Romney was way ahead of rival Republicans nationally, with 30 percent support. He still trailed Obama by five points in the White House race.
It was unclear how much damage had been done by attacks from opponents who accused Romney of being a job killer in the 1990s when he worked for Bain Capital, a firm that bought companies and restructured them.
Romney dug himself into trouble on Monday when he said: "I like being able to fire people who provide services to me," in discussing the need for greater competition between health insurance companies.
In a sharp departure for a party known as friendly to business, Republicans seeking to slow Romney seized on the comment to bash his business practices at Bain.
Gingrich, brooding over negative attacks from Romney and his backers that knocked him out of the front-runner position, has launched the toughest assault.
"Mitt Romney was not a capitalist during his reign at Bain. He was a predatory corporate raider," "When Mitt Romney Came to Town," a 27-minute video produced by a pro-Gingrich group, said.
The attacks prompted some conservatives to cry foul. The National Review magazine posted an editorial on Tuesday calling it "foolish and destructive" to attack Romney for his investment successes.
The onslaught took on new life during debates on Saturday and Sunday, too late to have much influence on the New Hampshire vote. And Romney retains a strong core of support in the small state of 1.3 million where he owns a summer home.
"I saw him work as a businessman. He sees what needs to be done and gets it done," said nurse Dennis Hamson, 58, as he voted in Londonderry, a southern New Hampshire town where many residents work in Massachusetts.
Results should start flowing in shortly after New Hampshire voting stations close at 7 p.m. EST (midnight GMT). About 250,000 people are expected to vote in the Republican primary while 75,000 are likely to vote to endorse Obama's re-election.
With some Republicans worried that Romney is too moderate on fiscal issues or topics like abortion and gay marriage, Romney had struggled to win more than about 25 percent support in national surveys on the nomination race.
Romney's rivals were mostly waging a fierce battle to win undecided voters to capture second place in New Hampshire. Santorum, who nearly won Iowa by appealing to social conservatives, has not seen that message resonate in New Hampshire.
Luke Breen, 52, a financial analyst, voted for Huntsman in Londonderry. He said he would not support a candidate who seemed intolerant. "He seemed to be more worldly," he said. "I know gay people and everyone has to have gay rights under our constitution."
Santorum and Texas Governor Rick Perry, along with Gingrich, are looking ahead to South Carolina on January 21, hoping to slow the man they call a "Massachusetts moderate" in the more conservative state.
"Most people see Romney as the establishment candidate, he's the establishment moderate," Santorum said on Fox News. "Going to South Carolina it's going to be different."
Gingrich backers have launched $3.4 million worth of ads in South Carolina.
A Suffolk University/7 News tracking poll had Romney at 37 percent in New Hampshire, versus 18 percent for Paul, 16 percent for Huntsman, 11 percent for Santorum, 9 percent for Gingrich and 1 percent for Perry. Seven percent of voters were undecided in the telephone survey Sunday and Monday, which had an error margin of 4.4 percentage points.
Additional reporting by Ros Krasny in Manchester and Patricia Zengerle and Jeff Mason in Washington; Writing by Patricia Zengerle; Editing by Donia Chiacu