AFP CHICAGO WHITE House hopeful Mitt Romney eyed a big win in President Barack Obama’s home state on Tuesday as he sought to clinch the Republican nomination and focus on November’s general election.

Polls across Illinois opened for the state primary at 6:00 am (1100 GMT) with former Massachusetts governor Romney the odds-on favorite to win.

Underdog Rick Santorum was pushing for an upset as he rallied conservatives to stay true to their principles rather than give their votes to a moderate just because he is the “choice of the establishment Republicans.” That upset appears unlikely, however, and a resounding win in Illinois would provide Romney with powerful momentum ahead of Louisiana’s primary Saturday and contests in Wisconsin, Maryland and Washington, DC on April 3
“Mitt Romney is headed for a blowout victory in Illinois,” Public Policy Polling said Monday, releasing a survey that showed Romney with a 15- point lead over Santorum, up from a nine-point lead in a Rasmussen poll released Friday.

Romney also has a commanding lead in the all-important delegate count as he seeks to be the Republican contender to take on Democrat Obama in the November 6 vote.

But Romney has been weakened by his failure to win over the party’s conservative base in the gruelling state-by-state primary race.

Written off in the early days, Santorum, a former Pennsylvania senator, has steadily notched up wins — 10 out of the past 31 contests — largely with the help of evangelicals and the party’s most conservative members.

Romney’s campaign has spent millions flooding the Illinois airwaves with negative ads calling Santorum an “economic lightweight” and “Washington insider” who has voted against his principles in the past.

Romney set his sights squarely on Obama in a speech at the University of Chicago on Monday in which he cast himself as the defender of conservative economic principles.

“For three years, President Obama has expanded government instead of empowering the American people,” he said.

“He’s put us deeper in debt.

He’s slowed the recovery and harmed our economy. And he has attacked the cornerstone of American prosperity: our economic freedom.” Santorum meanwhile wrapped himself in the cloak of late president Ronald Reagan — a conservative icon — and insisted Republicans could only beat Obama in November if they elect a “true conservative.” “There’s one candidate in this race who can never make this race about freedom because he simply abandoned freedom when he was governor of Massachusetts,” Santorum told supporters gathered in Reagan’s boyhood home of Dixon, Illinois on Monday.

“How can we nominate someone who can’t summon the energy, summon the vision, summon the greatness of our country and elevate the debate to something that is big and important and lasting,” Santorum said.

The candidates’ spouses have also joined the fray, with Santorum’s wife Karen defending her husband in a rare television interview with CNN, insisting he was prowomen and that he would not seek to block access to contraception despite his personal opposition to it.