Republican White House hopeful Mitt Romney sought to harness growing momentum on the eve of Super Tuesday and deal a hammer blow to rival Rick Santorum in the 10-state voting marathon, with all eyes on Ohio.

Voters in 10 states across America will have their say on Tuesday in what promises to be a pivotal day in the rollercoaster contest to see who will take on President Barack Obama, a Democrat, in the November 6 general election.

Ohio, a largely working-class swing state in the so-called Rust Belt that is crucial to Obama's reelection chances, is considered the big prize and Romney talked up its importance to voters, characterizing the race as a "battle for the soul of America."

"If you do your job tomorrow we're going to win this thing," he told cheering supporters at a rally in Zanesville.

Santorum, a devout Roman Catholic who fiercely opposes abortion and gay marriage, has billed himself as an authentic conservative who understands working class voters and can beat Obama in these Midwestern battlegrounds.

But a new poll released by Quinnipiac University gave Romney, the former governor of liberal Massachusetts, 34 percent support from likely Ohio primary voters, while Santorum, a former Pennsylvania senator, was at 31 percent.

The three-point margin makes the race too close to call. But the Quinnipiac University Polling Institute said the survey showed that the momentum was squarely with Romney, who one week ago trailed Santorum 36 to 29 percent.

"Just as he did in Florida and Michigan, Romney has erased a sizable deficit a week before the primary to grab the momentum in the final 24 hours," said Peter Brown, assistant director of the institute.

Romney, with five straight victories in Maine, Michigan, Arizona, Wyoming and Washington state, landed an important endorsement in the run-up to Super Tuesday, that of House Majority Leader Eric Cantor.

Cantor's nod, the first from a top member of the Republican congressional leadership, was seen as the strongest sign yet that the party establishment wants the bitter primary battle wrapped up soon.

The Romney campaign also announced the support of former attorney general John Ashcroft and another senior Republican senator, Tom Coburn of Oklahoma.

"I think more and more people are starting to see that it's time for Republicans to coalesce around a candidate... and begin to make our positive case rather than attacking one another," Senator Rob Portman told reporters at a Romney event in Youngstown, Ohio.

But Santorum, who came from far back in the pack in December to rival Romney for frontrunner status, played up his role as underdog in the race.

"The establishment is lining up behind the guy who's next in line," Santorum told supporters in a last-ditch appeal in Westerville, Ohio. "We have to have someone who can stand on principle, stand on ideas."

Romney, a former businessman who made his fortune as a venture capitalist, has pulled ahead in the early delegate count but Santorum and former House speaker Newt Gingrich loom in the wings as dark horses for the nomination.

Romney has won eight states, including a straw poll in Wyoming. Santorum has won three -- four, if what amounted to a beauty contest in Missouri is counted. Gingrich has won just South Carolina, while Texas congressman Ron Paul has no victories, though he hopes to do well Tuesday in the caucus states of Alaska, Idaho and North Dakota.

Delegates are awarded by each state in the complex Republican Party nominating process, sometimes on a proportional and/or non-binding basis, until one candidate reaches the 1,144 delegate threshold required for victory.

During a trio of campaign stops in Ohio on Monday, Romney focused on the economy, portraying himself as the leader who can help "reclaim the American dream" and Obama as a president who was in over his head, unable to pull the economic recovery out of neutral.

"These are tough times in America, and this president hasn't put out a jobs program to really get the economy going again," Romney told about 300 supporters at a factory in Canton that makes galvanized steel guardrails.

"What we need to talk about to defeat Barack Obama is getting good jobs and scaling back the size of government, and that's what I do. What I know is the economy. I spent my life in the real economy."

Gingrich, looking to reset his faltering bid, has pulled ahead in his home state of Georgia, while polls showed a tight contest between Romney and Santorum in Tennessee.

More than 400 delegates are up for grabs on Super Tuesday -- nearly 40 percent of the total needed to secure the nomination.