Republican presidential candidate Texas Gov. George W. Bush, left, and Michigan Gov. John Engler stand together as they answer questions during an interview for a national television morning show at the American Axle plant in Detroit Monday. (AP Photo)

DETROIT -- Republican presidential hopeful John McCain accused George W. Bush today of running a campaign by "character assassination" in the TV ads Bush is running leading up to Tuesday's Michigan primary.

Bush, saying he was "taking nothing for granted" in Michigan after his big weekend victory in South Carolina, focused on his economic proposals in a Detroit speech today. But he also took time to answer back to McCain's ridicule of his claim to be a reformer.

McCain had said Sunday, "Governor Bush is the governor of a state that has the most liberal campaign contribution laws. ... If Governor Bush is a reformer I'm an astronaut."

Bush said today that he is setting the pace in an important area -- posting contributors' names on the Internet almost as fast as their checks come in. He also criticized McCain for raising money from lobbyists after criticizing the impact of special interests.

McCain, speaking today at a townhall-style meeting in Traverse City, said Michigan voters "deserve better than the trash that's on your television set and over your radio" -- a reference to Bush ads, including one that chides McCain for comparing the Texas governor to President Clinton.

Michigan Republicans, McCain said, should "reject this negative campaigning, reject this character assassination, reject the low road to the presidency and support the high road."

Bush and McCain are competing for votes in primaries Tuesday in Michigan and Arizona. Michigan has emerged as a key test of McCain's viability in the race following his double-digit loss Saturday in South Carolina.

The Michigan race is close, according to a poll taken just before the South Carolina primary and polling done immediately afterward. A Detroit News poll taken last week found the two virtually tied and pollster John Zogby said today he found the same thing when he polled in Michigan Sunday.

"When McCain won in New Hampshire, it was huge and unexpected," he said, noting McCain's big bounce in South Carolina polls just afterward. "The results in South Carolina, perhaps, are not seen as something out of the ordinary."

Other than occasional public swipes at McCain, Bush, who attributed his South Carolina victory to a newfound aggressiveness, is reverting to a front-runner's posture of trying to ignore his rival and instead lay out his agenda for the country.

"It sounds like Senator McCain spent a lot of time talking about me, and I want to spend a lot of time talking about the future," Bush told reporters Sunday during a news conference in Southfield.

The stylistic differences came as the two competed with former ambassador Alan Keyes in Tuesday's GOP primary. The election will award 58 convention delegates, the biggest bounty to date in the 2000 campaign.

Today, McCain was traveling to Traverse City, Saginaw and Ypsilanti, Mich., before heading to his home state. Bush planned to stay in Michigan today, campaigning in Detroit, East Lansing and Grand Rapids.

After a run of early, isolated primaries, the campaign has gone national en route to "Super Tuesday." In elections on March 7, large states including California and New York will award almost 60 percent of the delegates needed for the nomination.

Bush is airing ads in California, Washington, North Dakota, Virginia, Michigan and Arizona. McCain was advertising in Michigan, Washington, California and Virginia.

That made Michigan, a classic swing state in general election campaigns, a critical battlefield in the nominating contest.

To Bush's advantage, the primary will be the first contest where he enjoys the institutional support of a fellow Republican governor, John Engler.

"It helps to have a governor who is popular and strong," Bush said. "It helps to have a group of friends who we both can call upon to turn out the vote, because this is a primary and primaries not only require a message and a messenger, but they require a ground game -- a grass-roots organization that has the capacity to take the energy and convert it to votes."

Exit polls in South Carolina showed that Bush's claim to be a "reformer with results" had connected, and also that voters believed McCain, more than his rival, had engaged in unfair attacks.

That left McCain with a tricky task of trying to underscore his conservative credentials at the same time he was angling to undercut Bush's claim of being a reformer -- all the while upholding his pledge to run a positive campaign.

Throughout Sunday, McCain ratcheted up his attack.

Appearing on NBC's "Meet the Press," the senator said Bush's record on spending compared unfavorably with President Clinton's.

"Spending in Texas has almost doubled, while spending under Clinton has been increased by 20 percent," he said.

Bush spokesman Ari Fleischer said spending increased only 2 percent under the governor when adjusted for inflation and a growing population. He added that the governor cut the rate of spending growth in half -- again adjusted for inflation and demographics.

McCain also picked up the endorsement of Rep. Peter King, R-N.Y., a former Bush supporter.