The $550,000 fine that the Federal Communications Commission imposed on CBS for Janet Jackson's ''wardrobe malfunction'' during the 2004 Super Bowl was a serious setback to freedom of expression. A federal appeals court threw out the fine last week, ruling that the agency violated its own standards for what constitutes indecency. It is a well-reasoned decision, and we hope that the Supreme Court, which will soon be taking up a similar case, will take as strong a stand for free speech.

Ms. Jackson's live performance ended with Justin Timberlake, in a deviation from the script, tearing part of her bustier and revealing her bare breast for nine-sixteenths of one second. The F.C.C. decided the broadcast was indecent because it depicted a sexual organ and violated ''contemporary community standards for the broadcast medium.'' The agency set aside its decades-old policy of not imposing fines for isolated or fleeting material.

The F.C.C. claimed that that policy applied only to words, not images. But the Philadelphia-based United States Court of Appeals for the Third Circuit rejected the claim. It ruled that the agency's decision to fine CBS was arbitrary and capricious -- and therefore illegal -- because it failed to provide a reasoned explanation, and appropriate notice, for its change in policy.

Last year, the New York-based United States Court of Appeals for the Second Circuit struck down the F.C.C.'s ''fleeting expletives'' policy. In that case, the F.C.C. had declared several broadcasts in which expletives were briefly uttered -- including a single word used by the singer Bono at an awards show -- to be indecent.

The two rulings, notes Andrew Schwartzman, president of the Media Access Project, confirm that the F.C.C.'s new approach to indecency was ''driven more by politics than logic.''

The F.C.C. rulings have had a serious impact on free expression. Because the agency's rules are so vague and the penalties so great, artists, writers and broadcasters have been censoring themselves. Last year, PBS offered two versions of Ken Burns's documentary ''The War,'' one deleting the coarse language often used in war for stations reluctant to risk fines.

It was cause for concern when the Supreme Court decided earlier this year that it would review the Bono ruling. That ruling was right on the law and an important blow for free speech. We hope the court affirms the Second Circuit ruling, and joins these two appeals courts in reining in the F.C.C.'s misguided censorship campaign.