CHICAGO (Reuters) - 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 Romney's campaign has argued that his rivals cannot catch him in the contest to pick a challenger to Democratic 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.
After an event at Google Inc.'s Chicago office, Romney praised a budget proposal by congressional Republicans that would sharply cut federal spending and said Obama had failed to put forward a credible plan to rein in government health and retirement benefits, which are projected to increase dramatically over the coming decades.
"It's very much consistent with what I put out earlier," Romney said of the Republican budget plan. "I think it's amazing that we have a president who three and a half years in still hasn't put a proposal out that deals with entitlements."
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.
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 in Illinois.
Santorum and Gingrich 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.
"Either Romney's going to win this outright or it's going to be chaos," Gingrich said on Fox News Radio. "I think that Romney will be a very weak candidate in the general election and I think that as people realize that it gets harder for him to be the nominee."
Romney has 521 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, with 54 to be allocated from Tuesday's voting, but Santorum will not be eligible to win many of them because he failed to meet deadlines to file a slate of delegates in some districts.
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 Monday 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.
"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 on Monday.
Santorum also said that "I don't care what the unemployment rate is going to be. It doesn't matter to me." He 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 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.
Writing by John Whitesides and Andy Sullivan; Editing by Eric Walsh and Paul Simao