WASHINGTON — GOP presidential candidate John McCain's campaign on Wednesday aired and defended a 30-second television ad that likens Democratic rival Barack Obama to Paris Hilton and Britney Spears.

"He's the biggest celebrity in the world," an announcer says as viewers see quick photos of Hilton and Spears cut into scenes from Obama's speech to 200,000 people in Berlin last week. "But is he ready to lead?"

The ad, the latest McCain effort to gain traction against Obama, notes the Democrat's opposition to offshore drilling and accuses him of favoring higher taxes on electricity.

But McCain aides acknowledged that the ad is as much about image as issues.

Campaign manager Rick Davis said the Spears and Hilton photos were included to "demonstrate that the focus of the Obama campaign has been as much to create that celebrity status of his as it is to discuss the hard issues that the American people are forced to debate during the course of this campaign."

"What we decided to do is find the top three international celebrities in the world," Davis added. "And I would say from our estimations, Britney and Paris came in second and third."

McCain adviser Steve Schmidt also chided Obama as "the biggest celebrity in the world."

"It's backed up by the reality of his tour around the world. He has many fans," Schmidt said. "The question that we are posing to the American people is this: Is he ready to lead yet? And the answer to the question that we will offer to the American people is no, that he is not."

The ad is airing in 11 closely fought states: Ohio, Colorado, Iowa, Michigan, Missouri, Nevada, New Hampshire, New Mexico, Pennsylvania, Virginia and Wisconsin.

Obama, campaigning in Missouri, told reporters he pays no attention to McCain's ads, "although I do notice he doesn't seem to have anything to say very positive about himself. He seems to only be talking about me. You need to ask John McCain what he's for and not just what he's against."

His spokesman Tommy Vietor, declining specific comment on the effort to link Obama with Spears and Hilton, did drop in a reference to a Spears song.

"On a day when major news organizations across the country are taking Senator McCain to task for a steady stream of false, negative attacks, his campaign has launched yet another. Or, as some might say, 'Oops! He did it again,' " Vietor said.

The ad also drew criticism from former longtime McCain adviser John Weaver, who told TheAtlantic.com that it seemed "childish" and "diminishes John McCain."

"John's been a celebrity ever since he was shot down (in Vietnam)," Weaver said. "Whatever that means."