GRAND RAPIDS, Mich. >> Mitt Romney hoped to avoid an embarrassing home-state loss in today’s Michigan primary but blamed his difficulty attracting needed support from the state’s conservative Republicans on his unwillingness "to light my hair on fire" to get their votes. 

Rival Rick Santorum, meanwhile, defended his campaign’s use of automated telephone calls encouraging Michigan Democrats to vote against Romney. He suggested that Romney did essentially the same thing earlier this year and should stop complaining. 

The last-minute flurry of activity came as voting got under way in Michigan’s critical Republican presidential primary. Arizona also was holding a GOP primary today but, with Romney favored to win, Michigan’s tossup contest was alone in the political spotlight.

The race is critical for both candidates. 

Santorum swept three states, including a nonbinding contest, on a single night early this month and another win, especially in the state of Romney’s birth, would keep his momentum going. Romney needs to avoid a potentially devastating setback in the state where he was raised and where his father, George, served three terms as a 1960s governor.

Asked by reporters why he’s struggling to win over his party’s right wing in his home state, Romney said it’s because he’s unwilling to say "outrageous things" like his opponents.

"It’s very easy to excite the base with incendiary comments. We’ve seen throughout the campaign that if you’re willing to say really outrageous things that are really accusative and attacking of President Obama, you’re going to jump up in the polls," Romney said during a stop at his campaign headquarters in Livonia. 

Answering questions for the first time in nearly three weeks from his traveling press corps, he said: "I’m not willing to light my hair on fire to try and get support. I am what I am."

Asked whether a series of comments by him highlighting his vast personal wealth were hurting the campaign, Romney said: "Yes. Next question." 

Santorum defended using the "robo-calls," saying his campaign is doing what it needs to do to win the vote. 

"We’re going to get voters that we need to be able to win this election. And we’re going to do that here in Michigan today," Santorum said outside a Grand Rapids-area restaurant. 

Romney has complained that the tactic is "deceptive and a dirty trick."

But Santorum, a former Pennsylvania senator, suggested that Romney did much the same thing by courting independent voters in New Hampshire’s GOP primary last month.

He also accused the former Massachusetts governor of employing his own "dirty trick" by running automated calls before the 2008 election that featured a recording of Santorum endorsing Romney. Santorum suggested that Romney stop complaining. 

"I didn’t complain about it. I don’t complain. You know what? I’m a big guy. I can take it," Santorum said.

Only Michigan Republicans may vote in today’s GOP primary, though party rules allow voters to change their affiliation temporarily on the spot. The potential involvement of Democrats adds a new twist to a contest already expected to have significant implications for Romney’s White House bid.

Romney, who spoke today with Fox News Channel, called the phone calls "outrageous and disgusting — a terrible, dirty trick." He accused Santorum of "teaming up with Barack Obama’s people" to derail the Romney campaign.

"This is a new low for his campaign and that’s saying something," Romney said. 

Neither Newt Gingrich nor Ron Paul actively competed in Michigan or Arizona. 

Romney was born and raised in Michigan, and his father was its governor. But Santorum’s rise in polls following the three-state sweep forced Romney to work hard in Michigan over the past week. He’s hosted nearly a dozen public events and he and his allies have spent more than $2 million on local television advertising.

Santorum campaigned today around Grand Rapids, in a western Michigan region that is home to many social conservatives and tea party supporters. He also darted to Ohio, one of 10 states voting on March 6, for a rally.

"I don’t trust him," Carol Alexander, of nearby Wyoming, Mich., said of Romney as she waited for Santorum to arrive at the Rainbow Grille in Grandville, Mich.

A self-described religious conservative, Alexander said she was leaning toward Santorum, whom she said "speaks what he believes."

Alexander said she’s been inundated with phone calls from campaigns and that "it’s been getting kind of nasty." But she discounted the impact of Santorum’s latest tactic.

"Do you really think a liberal is going to vote for Santorum?" she asked with a smile. "I don’t think they’re going to do it."

Romney spent part of the day in suburban Detroit, an area with a larger collection of the moderate Republicans who are a key segment of his support.

His overwhelming advantages in Michigan, however, may not pay off in a contest generally dominated by the Republican Party’s more conservative flank. He trailed Santorum by a significant margin in polls as recently as last week. But those surveys since have tightened and turned today’s election into a tossup.

Romney predicted victory Monday night as a crowd gathered at the Royal Oak Music Theatre waited to hear rocker-rapper Kid Rock perform.

"I’m going to win in Michigan and I’m going to win across the country," Romney said.

Santorum, perhaps in a nod to the recent swing in the polls, was more cautious as he spoke to voters in Lansing. 

"I think the fact that we are doing as well as we are is a pretty big deal in this state," he said.

Paul ended a three-state tour of Michigan on Monday. He planned to await today’s outcome in Virginia. Gingrich spent today campaigning in his home state of Georgia.

No matter the top finisher, Romney and Santorum stand to split the 30 delegates at stake in Michigan because the state distributes delegates proportionally. By contrast, Romney is favored to win all 29 delegates in Arizona, which features a winner-takes-all system. 

So far, Romney has 123 delegates to 72 for Santorum. Gingrich has 32 and Paul has 19, based on an Associated Press count. It takes 1,144 delegates to win the party nomination at the Republican National Convention in Tampa, Fla., this summer.