McCain's ad, titled "Celeb" and set to air in 11 battleground states, intercuts images of Obama on his trip to Europe last week with video of twenty-something pop stars Spears and Hilton - both better known for their childish off-screen antics.
"He's the biggest celebrity in the world, but is he ready to lead?" the voiceover asks, noting the Illinois senator's opposition to offshore oil drilling and suggesting he would raise taxes if elected.
It was the latest effort by the GOP hopeful to cast Obama as a lightweight with little experience in leadership or governing. It also was risky for McCain's campaign to both acknowledge Obama's worldwide fame and depict it as a weakness rather than a strength.
Campaigning in Missouri, Obama said the ad was the latest example of McCain's negativity - a theme his campaign has tried to stress lately.
"He doesn't seem to have anything positive to say about me, does he?" Obama said. "You need to ask John McCain what he's for, not just what he's against."
Obama also said the link to Hilton shows Republicans are leaving no stone unturned in their attempts to tarnish him.
"I've never even met the woman," he said.
The Obama campaign ad, released hours after McCain's, shows images of the Arizona senator with President Bush and accuses McCain of practicing "the politics of the past." The campaign said it could air as soon as Thursday.
It was the second Obama ad in as many days responding to negative spots by McCain. But it was unclear how broadly the campaign intended to run it. The campaign typically identifies states where its ads air, but on Wednesday only said this ad would appear "in some markets."
Kathleen Hall Jamieson, a communications professor at the University of Pennsylvania, said McCain's comparison of Obama to Spears and Hilton likely would not persuade many voters.
"The typical viewer will fail to see the analogy," she said. "Voters believe Sen. Obama is a celebrity, but not in the same sense as Britney Spears and Paris Hilton. So when you are asking, 'What are they doing in the ad?,' it distracts attention from the message of the ad."
McCain did not mention the ad at a town-hall meeting in Colorado, but reiterated many of his complaints about Obama.
"The beauty of his words have attracted many people, especially among the young to his campaign," McCain told workers at Wagner Equipment, which rents and sells heavy farm machinery. "My concern with Sen. Obama is with issues big and small. What he says and what he does are often two different things."
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Associated Press writers Jim Kuhnhenn in Washington and Mike Glover in Missouri contributed to this report.
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On the Net:
McCain: http://www.johnmccain.com
Obama: http://www.barackobama.com
