A federal appeals court struck down a Federal Communications Commission policy on indecency Tuesday, saying that regulations barring the use of “fleeting expletives” on radio and television violated the First Amendment because they were vague and could inhibit free speech.

The decision, which many constitutional scholars expect to be appealed to the Supreme Court, stems from a challenge by Fox, CBS and other broadcasters to the F.C.C.’s decision in 2004 to begin enforcing a stricter standard of what kind of language is allowed on free, over-the-air television.

The stricter policy followed several incidents that drew widespread public complaint, including Janet Jackson’s breast-baring episode at the 2004 Super Bowl and repeated instances of profanity by celebrities, including Cher, Paris Hilton and Bono, during the live broadcasts of awards programs. The Janet Jackson incident did not involve speech but it drew wide public outrage that spurred a crackdown by the F.C.C.

In a unanimous three-judge decision, the Court of Appeals for the Second Circuit in New York said that the F.C.C.’s current policy created “a chilling effect that goes far beyond the fleeting expletives at issue here” because it left broadcasters without a reliable guide to what the commission would find offensive.