(AP) - The question of whether Mitt Romney is conservative enough to deserve the Republican presidential nomination regained center stage in the GOP contest Sunday, with Rick Santorum saying the former Massachusetts governor fails the test. Santorum urged Michigan voters to turn the race "on its ear" by rejecting Romney in Tuesday's primary in his native state, in which Romney is spending heavily to avoid an upset. Santorum said Romney's record is virtually identical to President Barack Obama's on some key issues, especially mandated health coverage, making him a weak potential nominee. "Why would we give away the most salient issue in this election?" an impassioned Santorum told more than 100 people in a remote, snow-covered region of Michigan's Upper Peninsula. Santorum, a former senator from Pennsylvania, said he is the true conservative on fiscal and social issues. Romney rejected the claims. "The biggest misconception would be that I'm a guy that comes from Massachusetts and therefore I can't be conservative," Romney told "Fox News Sunday." In his one term as Massachusetts governor, he said, he balanced budgets, reduced taxes, enforced immigration laws, "stood up for traditional marriage" and was "a pro-life governor." "I'm a solid conservative," Romney said. The exchange highlighted the choice facing Republican voters in Arizona and Michigan on Tuesday, and another 10 states a week after that. Romney did pick up the endorsement of Arizona Gov. Jan Brewer on Sunday. Conservative activists dominate the GOP primaries. But party regulars fear too much focus on the Republican right will leave the eventual nominee poorly positioned to confront Obama in November, when independent voters will be crucial. Santorum, a hero to anti-abortion and home-schooling advocates, disputes that argument. The way to beat Obama, he said Sunday, is with an unvarnished conservative whose views dramatically clash with the president's on the economy, church and state, energy, foreign policy and other issues. He said the party needs "someone who can paint a very different vision of the country." Romney and Santorum hit Obama on many issues, including the president's apology for the actions of U.S. troops who burned Qurans - inadvertently, they said - while destroying documents on a military base in Afghanistan. Romney said that for many Americans, the apology "sticks in their throat." "We've made an enormous contribution to help the people there achieve freedom," he said. And for us to be apologizing at a time like this is something which is very difficult for the American people to countenance. As for U.S. troops in Afghanistan, Romney said Obama "made an enormous error by announcing the withdrawal date of our surge forces during the fighting season." Santorum portrayed Obama's apology for the burned Qurans as further proof that the president is trying to appease "forces of evil" bent on America's destruction. To apologize rather than simply note a mistake was made, he said, "not only encourages them, but I believe, incites them." Santorum criticized Obama in appearances on NBC's and ABC's Sunday talk shows, but he was more animated and emotional in his noon speech to voters in Marquette. He told them the president "has systematically taken every opportunity to try to take control of different sectors of the economy; tried to take your freedom and opportunity away from you and give it to people who know better than you how to run your lives, or your business." Santorum got a rare hostile question from Wally Tuccini, 57, a heavy equipment operator from Marquette. Tuccini said his mother was a Roman Catholic who personally opposed birth control, as does Santorum. When she delivered her eighth child, Tuccini said, the family was so poor they barely obtained essential medical care in time, and he asked why Santorum wants to reduce the government's social safety net. "We don't need a government health care plan to be able to solve the problem," Santorum replied. "What we need is a process in this country where people will have an opportunity to go out and use their resources, like we do in this country with housing," cars and clothing. Santorum noted that he supports a refundable tax credit for low-income people seeking health insurance. He did not offer details, nor does his campaign website. Romney, who campaigned Sunday in Traverse City, Mich., and Daytona, Fla., defended his proposal to cut income taxes across the board. "I want to make sure that we maintain the progressivity of the code," he told Fox News. And I want to help people who I think have been most hurt by the Obama economy - and that's middle-income Americans. Romney said he wants to "lower the marginal rate for all Americans." Former House speaker Newt Gingrich is not competing in Michigan. He attended church services Sunday in Georgia, where he launched his political career, and warned an audience that the "secular left" was trying to undermine principles established by the Founding Fathers. He said America had faced a "50-year assault" by those trying to alienate people of faith. Gingrich reiterated his criticism of Obama's apology for the burned Qurans. On NBC's "Meet the Press," Santorum said Romney and Texas Rep. Ron Paul, the fourth GOP presidential candidate, seemed to be secretly working together to undermine him. Santorum offered no proof, and predicted a long nominating process. Romney told Fox, "I'm convinced I'm going to become the nominee, and we'll be willing to take however long it takes to get that job done." Associated Press writers Kasie Hunt in Michigan and Ken Thomas in Georgia contributed to this report.