Romney and his chief rival, Rick Santorum, scrambled for any advantage they could find today in Ohio, the most-watched contest in the 10-state extravaganza stretching from Alaska to the southeast.

Latest polls found Santorum slipping in Ohio, putting him in a near dead heat with Romney, and Gingrich looking strong but not invincible in his home state of Georgia, which he needs to win to have any hope of resurrecting his candidacy. Ron Paul, trailing the delegate count and the expectations game, hoped one or more of the three caucus states, Alaska, Idaho and North Dakota, would finally give him a victory.

Fully one-third of the delegates needed to clinch the nomination are at stake Tuesday, altogether a larger prize than all the previous primaries and caucuses combined.

On the eve of Super Tuesday, the message coming from Republican establishment figures was clear: It’s time, if not past time, to crystallize the competition and unite the party behind the effort to defeat President Barack Obama in the fall.

House Majority Leader Eric Cantor of Virginia and Oklahoma Sen. Tom Coburn, one of the most conservative members of the Senate, were among the latest GOP luminaries to swing behind Romney. Conservative John Ashcroft, attorney general in the George W. Bush administration and a former Missouri senator, threw his support behind Romney today. “No other candidate stands out for his executive leadership experience or ability to accomplish difficult task as does Mitt Romney,” he said.

Cantor told CNN “we’re coalescing around Mitt Romney’s plan to actually address the economic challenges,” and “trying to find ways to work together and bring people together and set aside differences.”

Whether Super Tuesday marks that sort of turning point remains to be seen. Romney has been the presumed long-haul favorite from the start but Santorum’s surge unfolded as the latest in a line of surprises from a field now down to four candidates.

Santorum told The Associated Press on Sunday that Romney’s inability to wrap up the nomination, despite an enormous financial advantage, “raises a lot of questions in people’s minds whether this is the man who can unite the party and be effective as a foil against Obama.”

He suggested that the GOP nomination may not be settled until this summer’s party convention, a circumstance considered improbable despite the jumble so far.

While Romney has a significant advantage in northeastern states such as Vermont and Massachusetts — where he was governor — and Santorum is strong in conservative states such as Oklahoma, Ohio tops the list of hotly competitive and delegate-rich contests Tuesday. Both candidates focused on the state today after a weekend swing through the South. Gingrich planned three stops in Tennessee today.

Romney has been working to make the race about the economy and to avoid intensifying the debate over conservative social values, a strong suit for Santorum. That effort was not helped when conservative radio host Rush Limbaugh called a Georgetown University law student a “slut” and a “prostitute” on his nationally syndicated radio program. The woman testified at a congressional hearing in favor of an Obama administration mandate that employee health plans include free contraceptive coverage. He apologized but the furor continues.

Arizona Sen. John McCain, the 2008 Republican presidential nominee, denounced Limbaugh’s comments today, saying the remarks “should be condemned” by people across the political spectrum. The 2010 GOP candidates have dissociated themselves from Limbaugh’s comments, though not as forcefully as McCain did on CBS’ “This Morning.”

Romney has won four consecutive contests, including Saturday’s Washington caucuses. His broad, well-disciplined organization all but assures he’ll collect more delegates than his opponents on Tuesday, in contrast with Santorum’s looser group of supporters. Santorum and Gingrich did not collect enough signatures to qualify for the Virginia ballot, for example, and Santorum cannot win 18 of Ohio’s 66 delegates for similar reasons.

All told, 419 delegates are at stake Tuesday. Romney leads with 203 delegates from previous contests, Santorum has 92, Gingrich has 33 and Paul, 25. It takes 1,144 delegates to win the nomination.