Washington (CNN) -- Mitt Romney and Rick Santorum made their final push for votes Monday on the eve of primaries in Arizona and Michigan, as new polls indicated that the Republican presidential race remains close and volatile.
After a relative lull in the campaign, Tuesday's primaries bring new focus and urgency to the campaigns of front-runners Romney and Santorum as well as trailing candidates Newt Gingrich and Rep. Ron Paul.
For Romney, Michigan amounts to a vital test because the state is considered home turf, due to his childhood years there while his father George was governor.
A Romney victory in Michigan would probably cement his status as the presumptive nominee, while a victory for the recently resurgent Santorum would raise further questions about Romney's ability to attract broad conservative support in later primaries or against President Barack Obama in November's general election.
Romney made clear Monday that the Michigan outcome is important, telling supporters in Rockford to rally their neighbors to help him on Tuesday.
"This is a critical time, you guys. I need your vote," he said.
Romney also took a shot at Santorum, calling him "a nice guy" but adding that "he has never had a job in the private sector."
"He has worked as a lobbyist and worked as an elected official, and that's fine," Romney said. "But if the issue of the day is the economy, I think to create jobs it helps to have a guy as president who has had a job, and I have."
Santorum fired back at Romney at an event in Lansing, depicting himself as a longtime fighter for conservative causes, compared with "the other candidate who is running here in Michigan at the top of the polls."
He also took aim at Obama, blaming the president for blocking the expansion of domestic energy production to cause gas prices to increase.
However, Santorum included a dubious claim that high gas prices, rather than suspect lending practices or complex Wall Street trades, torpedoed the housing market in 2008 to trigger a recession.
"We need to look at the situation with gas prices today," Santorum said. "We went into a recession in 2008 because of gasoline prices. The bubble burst in housing because people couldn't pay their mortgages because they were looking at $4 a gallon gasoline."
When questioned later by reporters, Santorum backtracked slightly, insisting that energy prices were a factor in the recession while apologizing and saying he would "make sure that I will be much more specific when I talk about it."
In a Wall Street Journal opinion piece Monday, Santorum proposed simplifying the tax code and cutting $5 trillion from the federal budget over five years.
"I'll work with Congress and the American people to once again create an economic environment where hard work is rewarded, equal opportunity exists for all, and families providing for their children can once again be optimistic about their future," Santorum wrote.
Romney responded by welcoming the focus on economic issues, rather than social issues such as religious freedom and female contraceptives that Santorum has emphasized in recent days.
"I am glad he recognizes this is going to be a campaign about the economy," Romney said. "It is time for him to really focus on the economy and for you to all say, 'OK, if the economy is going to be the issue that we focus on, who has the experience to actually get this economy going again?' "
A new poll Monday of likely Republican primary voters in Michigan showed Santorum at 36% support for a slight but statistically insignificant lead over Romney's 35%, while Paul and Gingrich were well back.
According to the American Research Group poll, conducted Saturday and Sunday, Santorum has lost 2 percentage points since a similar survey conducted February 21-22, while Romney has gained 1 percentage point.
Other polls also showed a tightening race between Romney and Santorum, who came from well back to seize the lead after his trifecta of victories February 7 in Colorado, Missouri and Minnesota.
The latest Gallup national tracking poll showed that Romney has erased a 10-point deficit against Santorum among registered Republicans, with 31% of respondents saying they would support Romney and 29% favoring Santorum.
That reversed 36% to 26% advantage for the former Pennsylvania senator over Romney last week. Another nationwide poll released Monday, addressing likely GOP voters nationwide, also suggested that the pair have roughly equal support now.
The Politico/George Washington University Battleground Poll showed Santorum with 36% support among likely GOP voters, while the former Massachusetts governor had 34% -- well within the survey's margin of error.
Despite the tight poll numbers, a senior Santorum adviser appeared to downplay the importance of a victory in Michigan, saying "we have already won" by forcing Romney to devote major time and resources in the state.
"No matter what the results are, we've won. This is Romney's home state," said the adviser, John Brabender.
Even with the drop in Santorum's lead, Brabender said the fact that Romney is scrambling to win his native state means he will have fewer resources for subsequent battles, including the 10 states and 437 delegates at stake on Super Tuesday, March 6.
Brabender also said Santorum has achieved his goal of establishing himself as the major conservative challenger to the more moderate Romney in the Republican race.
Meanwhile, a Democratic strategist said Monday that he was trying to get Democrats to support Santorum in Michigan's open primary as a way to hurt Romney.
"Democrats can get in there and cause havoc for Romney all the way to the Republican convention," said the strategist, Joe DiSano. "If we can help set that fire in Michigan, we have a responsibility to do so."
DiSano said he has gotten about 12,000 commitments from Democrats to go to the polls and vote for Santorum.
However, Michigan Republican Party spokesman Matt Frendeway downplayed the idea of Democratic voters having a real impact on the GOP primary, saying, "I don't think this will move the needle at all."
Paul, the libertarian champion who has a devoted but limited support base among mostly young followers, was also campaigning in Michigan on Monday. The Texas congressman has waged a strategic campaign aimed at accumulating delegates so he can assert influence at the Republican convention in August.
Gingrich, the former House speaker, was alone in skipping Michigan on Monday. He is banking on a strong Super Tuesday performance in the Southern states of Georgia, which represented in Congress, and neighboring Tennessee to revitalize his flagging campaign.
However, a recent poll showed Santorum well ahead in Tennessee, with Gingrich far back -- an outcome that would put Gingrich's campaign in jeopardy. Santorum also is leading in Ohio, another Super Tuesday state, according to recent poll numbers.
Gingrich, whose support among registered Republicans in the Gallup poll grew 2 percentage points to 15% in the past week, was scheduled to campaign in Tennessee on Monday.
Santorum and Gingrich are vying to be the main conservative challenger in the Republican race.
In his push for conservative support, Gingrich warned Sunday in remarks at a Georgia church that liberal elitism is threatening the country.
"You have elites in the bureaucracy, elites in the judgeship, frankly elites in the news media, elites in the academic world and elites in politics -- and they would all like to impose on us an America that none of us believe in," Gingrich said.
Romney's advantage in money and organization have helped him fend off challenges from a succession of Republican contenders.
On Sunday, Romney surrogates appeared on talk shows to boost his chances ahead of the upcoming contests.
New Jersey Gov. Chris Christie, a strong Romney backer, declared on the CBS program "Face the Nation" that "Rick Santorum's not going to be the nominee," while Sen. John McCain of Arizona said on CNN's "State of the Union" that he is "confident Mitt will do well on Tuesday night in Arizona and in Michigan, and hopefully that will move this process forward so we can concentrate on the real adversary."
Another veteran Senate Republican, Lindsey Graham of South Carolina, also said on the CNN program that he expects Romney to win both states Tuesday.
While Graham has yet to endorse a candidate, he praised Romney for "getting better and better" throughout the campaign season.
Romney made a rare talk show appearance on "Fox News Sunday" in which he parried questions about what critics call his inability as a wealthy businessman to connect with working-class Americans such as tea party conservatives.
Last week, Romney's comment that his family owns several cars kept at different residences, including two Cadillacs driven by his wife, came under media scrutiny.
"You know, I can't be perfect. I just am who I am," Romney said on the Fox program, adding: "If people think that there is something wrong with being successful in America, then they better vote for the other guy, because I've been extraordinarily successful, and I want to use that success and that know-how to help the American people."
In appearances on ABC and NBC, Santorum was questioned about comments last week that challenged the call more than 50 years ago by former President John F. Kennedy -- the nation's first Roman Catholic president -- for an absolute separation of church and state.
On ABC, Santorum said the Kennedy speech -- which sought to ease concerns about his faith interfering with his ability to govern -- made him sick.
"What kind of country do we live that says only people of non-faith can come into the public square and make their case?" Santorum said in seeking to link his interpretation of the Kennedy speech with his criticism of the Obama administration for what he calls impeding on religious freedom.
"That makes me throw up, and it should make every American who has seen from the president, someone who is now trying to tell people of faith that you will do what the government says, we are going to impose our values on you," Santorum said, later adding that imposition of government values would be "the next logical step when people of faith, at least according to John Kennedy, have no role in the public square."
CNN's Peter Hamby, Dana Bash, Eric Marrapodi, Paul Steinhauser and Michael Pearson contributed to this report.