Surprise caller Howard Stern ambushed Federal Communications Commission Chairman Michael K. Powell during a San Francisco radio talk show yesterday, accusing him of nepotism, racketeering and possible retribution against the ranting shock jock's employer, Infinity Broadcasting, for the phone call.

"You kind of sit there and you're the judge and the arbiter and you're the one who tells us what we can and can't say on the air and I really don't think you're qualified to be the head of the commission," Stern said. "Do you deny that your father got you this job?" he asked, referring to Secretary of State Colin Powell.

"I deny it exceedingly," responded Powell, who was a lawyer in private practice and in the Justice Department's antitrust division before joining the FCC seven years ago and becoming chairman in 2001. "I think it's a little unfair that just because I have a famous father and other public officials don't that you make an assumption that that's the only basis in which I serve in my position."

The two talked for about 10 minutes during KGO-AM's morning show, hosted by Ronn Owens. The exchange was posted on KGO's Web site.

"Does it make you nervous to talk to me?" asked Stern.

"It does not," said Powell, who raised his voice only when he called Stern's remarks about his father a "cheap shot."

In an e-mail exchange with The Post last night, Powell said he believes the run-in was the first time the two men have spoken. Stern has invited Powell to be a guest on his radio show.

Stern painted Powell as a muzzler of free speech, but Powell pointed out that all of the recent indecency fines were passed unanimously by the five-member commission and that the body's two Democratic commissioners -- Michael J. Copps and Jonathan S. Adelstein -- argued that the fines should have been stronger. The Democrats, not the three Republican members, have argued for license revocation for indecency violations, rebutting Stern's assertion that "if I were a friend of George W. Bush, you-know-who would give the word and you'd back off from me."

"I respect your opinion, but you personalize it as if you're answering to me," Powell said. "You're answering to the commission, if you're answering to anybody. . . . Congress just [increased] indecency fines and that passed the Senate, 99-1. There's not 99 Republicans and one Democrat in the Senate."

Stern recently signed a five-year, $500 million contract with Sirius Satellite Radio, which he plugged several times during the exchange. Satellite radio, like cable television, is not subject to FCC indecency regulations. Stern's deal begins when he leaves Infinity in January 2006.

Infinity is owned by Viacom Inc., which also owns CBS, and Stern said that former Viacom president Mel Karmazin once told him that Viacom had to pay indecency fines caused by Stern before the FCC would renew its radio and television licenses.

"That is flatly false," Powell said. "That's a lie."

Infinity paid the FCC $1.7 million in 1995 to settle fines incurred by Stern's show, and Clear Channel Communications recently paid $1.75 million to settle a number of fines, some caused by Stern.

"I really don't think you're qualified" to head the commission, Stern, left, told Michael Powell, above.