RACINE, Wisconsin (Reuters) - Republican White House hopeful John McCain accused Democrat Barack Obama on Thursday of playing racial politics in some of the most biting back-and-forth of the presidential campaign.

The negative twist in the campaign for the November 4 election was prompted by a McCain television advertisement on Wednesday that called Obama a celebrity akin to star-crossed U.S. personalities Britney Spears and Paris Hilton.

In response, Obama said McCain was trying to scare voters away from him by pointing out he had “a funny name, and he doesn’t look like all the presidents on the dollar bills and the five dollar bills.”

Obama, whose father was Kenyan, would be the first black U.S. president. Only white men, most of them former presidents, are on U.S. paper currency.

“Barack Obama has played the race card, and he played it from the bottom of the deck. It’s divisive, negative, shameful and wrong,” McCain campaign manager Rick Davis said in a written statement.

McCain agreed with Davis, telling reporters he was “very disappointed” that Obama had used the race card.

“Race will not have any role in my campaign, nor is there any place for it. I’m disappointed that he’s used it.”

He dismissed Democratic charges he was taking the low road, saying Obama had “run negative ads on me continuously, and I might point out for the record that his was the first.”

Obama fired back during a town hall meeting in Cedar Rapids, Iowa, that the attacks did not help voters deal with the array of problems they face.

Republican presidential candidate Senator John McCain is shown during an energy policy speech at the University of Nevada Las Vegas, June 25, 2008. REUTERS/Steve Marcus/ Las Vegas Sun

“You’d think we’d be having a serious debate but so far all we’ve been hearing about is Paris Hilton and Britney Spears. I do have to ask my opponent: Is that the best you can come up with?” the Illinois senator said.

He said McCain had pledged to run an honorable campaign but had fallen back into “these negative ads, these negative attacks.”

At a later fundraiser in Houston, Obama called the McCain attacks “intellectually bankrupt.”

“Our politics is small when we need to be thinking big,” he said. “The times are serious. It calls for serious people.”

McCain defended the ad when a woman asked him about it at a town hall meeting in the battleground state of Wisconsin.

The woman said the tone of the ad did not square with his earlier promises to avoid “mudslinging” and asked him whether he was now flip-flopping.

McCain said, “We’re proud of that commercial.”

“I admire his (Obama’s) campaign, but what we are talking about here is substance and not style. And what we’re talking about is who has an agenda for the future of America. Campaigns are tough, but I am proud of the campaign that we have run,” McCain said.

UNDERDOG

The McCain campaign is trying to shake up a race that currently favors Obama at a time when the U.S. economy is weak, the U.S. military is stretched fighting two wars, and the annual budget deficit is approaching a half-trillion dollars.

The McCain campaign believes the 71-year-old Arizona senator is the underdog but that the race is close. It is trying to paint Obama as an inexperienced lightweight.

McCain went through a point-by-point litany of questions about Obama’s positions on taxes, energy and the Iraq war.

Noting Obama’s opposition to offshore oil drilling, he said his Democratic rival had urged Americans to make sure their tires were properly inflated as a way to increase gas mileage.

“Yesterday, he suggested that we put air in our tires to save on gas. My friends, let’s do that. But do you think that’s enough to break our dependence on Middle Eastern oil? I don’t think so,” he said to chuckles from the crowd.

The “celebrity” television ad showed spliced images of Spears and Hilton with video of Obama addressing 200,000 people in Berlin last week.

The Obama camp launched a Web site called “The Low Road Express” to respond to what it considers inaccurate ads and statements from McCain.

Obama adviser Robert Gibbs said on NBC’s “Today” show that “the McCain campaign has very clearly decided that the only way to win this election is to become very personal and very negative. We believe that people will see that as nothing more than the same old politics and the same old policies of the last eight years.”

Both candidates vying to succeed President George W. Bush have said in the past they planned to run campaigns that would stay away from the negative attacks that marked some presidential contests in recent years.