White House hopefuls Mitt Romney and Rick Santorum battled over who was the most conservative Republican on Saturday -- while knocking President Barack Obama on account of accelerating gasoline prices -- as the high-octane race in Michigan moves toward a still-uncertain finish.

With only a couple of days to go before primary-election voting begins on Tuesday in the state where Romney was raised, the two top contenders worked to bolster local support in a bid to keep momentum as the unpredictable race for the Republican presidential nomination rounds the next bend.

The former governor of Massachusetts and longtime front-runner for the nomination, Romney has the most to lose should Michigan fall out of his grasp.

A Santorum win in the Rust Belt state would be a sharp blow to Romney's political standing, already dented by the former U.S. senator from Pennsylvania's comparatively recent victories in Colorado, Minnesota, and Missouri.

But a lackluster performance by Santorum in Wednesday's Republican debate and concern among party stalwarts about his electability have given Romney an opening.

An average of polling data by RealClearPolitics showed Romney with a slight lead over his chief rival in Michigan. In Arizona -- whose primary contest will also be conducted on Tuesday -- Romney was projected to beat Santorum handily.

Santorum is attempting to regain his footing. At a campaign event in Troy, he criticized Romney for supporting a government bailout of Wall Street but opposing one for Michigan's car companies. He told a supportive crowd that his consistency as a leader trumped Romney's back-and-forth on policy issues.

What you have with me is what you see is what you get as opposed to, well, what you see today may be different than what you get tomorrow, Santorum said. You have an opportunity here in Michigan to shock the country.

Romney hammered Santorum for a comment he made during Wednesday's debate, when he defended voting for a proposal he opposed because, in Washington, when you're part of the team, sometimes you take one for the team leader.

Romney has pounced on that comment ever since as proof of his claim that Santorum was a free-spending Washington insider.

We can't continue to take one for the team. My team is the people of the United States of America, and I'm going to fight for that team, not the partisans in Washington, Romney said in Troy. We have to have principled conservative leadership, and I have demonstrated that in my life and demonstrated it as governor.

Eye on Obama, Gasoline Prices

When not turning their sights on each other, Santorum and Romney lambasted Obama over rising gasoline prices, which have reached record highs for the month of February.

I don't know how stupid [Obama] thinks America is, Santorum said at an event on Friday night. Blaming everybody but himself for policies which, let's be honest, were intentional to drive up the cost of [gasoline].

The Democratic president went on the offensive over gasoline prices on Thursday, saying during a speech in Florida that American voters would not be fooled by politicians' promises of a magic bullet to bring down the cost of fuel.

Although Obama is not in a nominating fight like his would-be Republican rivals, the president's campaign has increased its visibility in Michigan before Tuesday's vote.

This week, it released an ad highlighting Obama's efforts to rescue the auto industry. Both Romney and Santorum opposed the government bailouts.

When the industry was on the verge of collapse, and others advocated letting 'Detroit go bankrupt,' President Obama helped save more than 1.4 million jobs up and down the supply chain by providing rescue loans to GM and Chrysler, the Obama campaign said in a release about the ad. Those loans allowed the industry to continue providing jobs to Americans and producing cars.

The president will continue to press that advantage next week. He plans to address a United Auto Workers conference in Washington on Tuesday, the day of the Republican primary, which will ensure that his support for the industry gets coverage on the same day as his rivals' race.

(Writing by Jeff Mason; Editing by Doina Chiacu)