Front-runner Mitt Romney appeared poised to widen his lead in the Republican presidential race with a victory on Tuesday 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 campaign for the White House and persuade 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 Democratic President Barack Obama in the Nov. 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 Representative 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 Monday.

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, but Santorum will not be eligible to win many of them because of his campaign's failure to satisfy the primary's complex rules.

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 on M onday to highlight his ability to lead the United States through an economic recovery.

'Get us out of this mess'        

"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.

"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 said that "I don't care what the unemployment rate is going to be. It doesn't matter to me." H e backed away from the comment later, telling reporters the success of his bid would not hinge on the jobless rate.

Romney has been unable so far to translate his substantial war chest and strong organization into broad support.

Some 63 percent of Republicans have a favorable view of Santorum, while 58 percent view Romney favorably, according to an ABC News/Washington Post poll released on Tuesday. Santorum enjoyed stronger support from conservatives, while Romney did better with moderates.

Both candidates face negative ratings among the broader voting public, the poll found.

The bitter, drawn-out Republican primary battle has exposed a stubborn rift between grassroots conservatives and the party's establishment, but Republicans of all stripes say they will have no trouble uniting behind the eventual nominee.

"The most important thing: Stopping Obama, period. The man is a communist. The man is a dictator," said Ed Freers, a retired jeweler from East Moline.

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.