CHICAGO (Reuters) - Front-runner Mitt Romney appears poised to widen his lead in the Republican presidential race with a victory on Tu esday in Illinois, where polls show he has a comfortable edge over top rival Rick Santorum.
Romney hopes a solid win in Illinois will give him a fresh burst of momentum in the volatile White House campaign and add urgency to calls for Republicans to rally around the former Massachusetts governor and end an increasingly bitter nominating battle.
Romney has more than twice as many delegates to the nominating convention as Santorum, and his campaign has argued that his rivals cannot catch him in the race to pick a challenger to President Barack Obama in the November 6 election.
Two Illinois polls on Monday gave Romney double-digit leads over Santorum, a former U.S. senator from Pennsylvania. A Public Policy Polling survey said Romney led Santorum by 15 percentage points, and an American Research Group poll put the lead at 14 points.
The other two contenders still in the race, former U.S. House of Representatives Speaker Newt Gingrich and libertarian Congressman Ron Paul, lagged badly in both polls.
Santorum, a staunch social conservative who has attacked Romney as too moderate to lead the party against Obama, shrugged off the polls and held on to hopes for an upset that would dramatically reshape the race.
"I predict if you are able to do what I know most people think is impossible, which is carry the state of Illinois, that will fundamentally change this election like no other contest to date," Santorum told reporters on Mon day.
Santorum and Gingrich, a fellow conservative, hope to keep Romney from capturing a majority of delegates by the time the nominating contests end in June, leaving the choice up for grabs among the party's mostly conservative delegates heading into the August nominating convention in Tampa, Florida.
Romney has 518 delegates to Santorum's 239 in the race for the 1,144 needed to win the nomination, according to a count by CNN. There are 69 delegates up for grabs in Illinois on Tuesday, although Santorum failed to file delegate slates in four congressional districts, cutting into his potential haul.
Romney and Santorum launched a new round of attacks on each other ahead of the vote, with Romney calling his rival an "economic lightweight" and Santorum accusing Romney, the former head of a private equity firm, of being "a Wall Street financier" who would have a hard time winning in November.
Romney has emphasized his experience in business, and he gave a speech on economic issues in Chicago o n M onday to highlight his ability to lead the United States through an economic recovery.
"I am running for president because I have the experience and the vision to get us out of this mess," Romney said.
But Santorum, who has campaigned heavily in rural southern Illinois and courted conservatives who distrust Romney for the moderate stances he took as governor of liberal Massachusetts, tried to turn that argument against Romney on Monday.
"What kind of conservative says, 'I'm the guy because of my economic experience that can create jobs'? I don't know. We conservatives generally think government doesn't create jobs," Santorum said.
Santorum also claimed at one point that "I don't care what the unemployment rate is going to be. It doesn't matter to me," but he backed away from the comments later to reporters.
"Of course I care about the unemployment rate. I want the unemployment rate to go down, but I'm saying my candidacy doesn't hinge on whether the unemployment rate goes up and down," he said.
Some Santorum supporters said they felt more comfortable with him because of his conservative principles.
"This is the first time in my lifetime that I trust a candidate and agree with him on the issues," said Peter Scordato, a Rockford, Illinois, small business owner who described Santorum as "one of us."
Santorum will head to his home state of Pennsylvania on Tuesday night to celebrate the Illinois returns with supporters in Gettysburg. Romney will hold his election-night party in Chicago.
After Illinois, the race moves to the conservative southern state of Louisiana on Saturday, where Santorum expects to do well. It then heads to Maryland, Wisconsin and the District of Columbia on April 3.
Additional reporting by Sam Jacobs; Writing by John Whitesides; Editing by Eric Walsh