But the GOP hopeful defends comparing the Democratic candidate to the heiress and pop star Britney Spears

Barack Obama just another Britney Spears or Paris Hilton?

Not John McCain’s best shot, says the Democrat’s camp after the Republican likened him to the two celebrities in a new commercial.

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“On a day when major news organizations across the country are taking Sen. McCain to task for a steady stream of false, negative attacks, his campaign has launched yet another,” says Obama spokesman Tommy Vietor. “Or, as some might say, ‘Oops! He did it again.'”

Counter’s McCain campaign strategist Steve Schmidt: “It’s beyond dispute that [Obama] has become the biggest celebrity in the world. But do the American people really want to elect the biggest celebrity in the world?”

In the ad, images of Spears, Hilton and Obama appear on the screen as a voiceover says, “He’s the biggest celebrity in the world. But is he ready to lead?”

McCain’s campaign manager says they chose to include Spears and Hilton in the ad because the women’s names came up second and third in a search for the top three international celebrities in the world.