| DAYTON, Ohio
DAYTON, Ohio Rivals Mitt Romney and Rick Santorum made their final pitch for support in the vital battleground state of Ohio on Monday, the day before 10 states hold Super Tuesday nominating contests that could be pivotal in an unpredictable Republican presidential race.
Romney has been gaining on Santorum in polls in Ohio all week, erasing a double-digit lead for the former senator from Pennsylvania. Three new surveys on Monday showed a tight race: one gave Romney a slight edge, one had Santorum with a small lead and the third showed a dead heat.
Ohio is the largest battleground and most closely watched prize of the 10 contests on Super Tuesday, the biggest day of voting in the Republican race to find a challenger to President Barack Obama in the November 6 election.
At campaign rallies and in a conference call with reporters, Santorum kept up his attacks on Romney for backing an individual mandate to purchase insurance in the Massachusetts healthcare plan, a precursor of Obama's federal overhaul.
Santorum said Romney's support for the mandate when he was governor of Massachusetts and in a 2009 USA Today column "forfeits the biggest issue in this campaign" against Obama and was evidence of why he could not win the support of conservatives.
"What you have with Governor Romney is someone who is simply not the genuine article. He's not someone you can trust on the issue of big government," Santorum told reporters.
Santorum said at a campaign rally in Westerville, Ohio, that Romney's views on the healthcare mandate would be a "drumbeat" during the campaign.
"Governor Romney supported a mandate at the very time it was being debated in the halls of Congress," he said. "You don't think it'll be used against him?"
Romney, who backs a repeal of the federal law, has said he supported the mandate in Massachusetts but did not believe the federal government should dictate a one-size-fits-all approach to states on healthcare.
At a morning stop in Canton in industrial northeast Ohio, the former head of private equity firm donned a hard-hat to tour a factory. Later in Youngstown, Romney pledged to focus his presidency on economic recovery.
He also took a shot at Santorum and his days in the Senate.
"We need to have a president who understands the economy if we're going to fix the economy. And my understanding of the economy and jobs did not come by reading about it or debating it in a subcommittee meeting," Romney said. "My experience in the economy actually came by living in the economy."
Romney is riding a wave of momentum into the Super Tuesday contests from a five-state winning streak capped by victories last week in Michigan, Arizona and Washington. A win in Ohio, a crucial state in the general election, would put him back in firm command of the race despite lingering doubts about him from conservatives.
A Santorum win in Ohio would turn the frequently shifting race upside down again. He also is aiming for victories in conservative Oklahoma and Tennessee.
Romney is favored in Vermont and Massachusetts, as well as Virginia, where Texas Congressman Ron Paul was the only other candidate to qualify for the ballot. Paul is hoping to score his first win in Alaska.
Polls show former House Speaker Newt Gingrich with a big lead in Georgia, which he represented in the House of Representatives. Gingrich said he also hoped to win delegates in Ohio as all four of the remaining candidates chase the 1,144 delegates needed for the nomination.
"It's very fluid and I think beginning to really move in our direction," Gingrich said on CNBC. "I think as things sink in you'll see me once again coming back and getting ahead. A lot of this is just momentum."
Obama scheduled a news conference at the White House for Tuesday morning, hoping to steal some of the spotlight from his Republican rivals who have dominated political headlines for months with their frequently shifting battle.
In Ohio, a Quinnipiac University poll on Monday showed Romney ahead of Santorum, 34 percent to 31 percent. A Suffolk University poll gave Santorum the narrow lead, 37 percent to 33 percent. Both leads were within the margin of error.
A CNN poll showed Romney and Santorum deadlocked at 32 percent each.
"The margin makes the Ohio race too close to call, but Romney is the one with the wind at his back," Quinnipiac pollster Peter Brown said.
Romney also has overtaken Santorum in Gallup's latest national survey. Romney leads by 38 percent to 22 percent in the poll released on Monday. Santorum led by 10 percentage points in a February 20 survey.
Santorum and his backers are being outspent in Ohio by about four-to-one by Romney and his Super PAC allies, according to PAC officials and media buyers who track campaign spending.
"To suggest this is David and Goliath is probably an understatement," Santorum told reporters, vowing he would run "very, very well in every one of those" Super Tuesday states.
"We feel confident we'll come out of Super Tuesday with what will be clear - there is one conviction conservative, there is one conservative you can trust," Santorum said.
(Additional reporting by Susan Heavey, Sam Jacobs and Sam Yougman; writing by John Whitesides; editing by Alistair Bell and Mohammad Zargham)