For the first time in a generation, the U.S. Supreme Court will set the standard for when networks can be fined for allowing curse words on the public airwaves.

In what promises to be a major First Amendment case, the Supreme Court announced yesterday it will hear a case involving Federal Communications Commission efforts in the past several years to take a hard line against errant curse words, even when the profanity is uttered during unscripted, live broadcasts. Last year, a federal appeals court in Manhattan ruled against the FCC’s move to institute a stricter policy, questioning whether occasional slip-ups cause enough harm to children in the audience to warrant government regulation.

The Supreme Court’s ruling, whatever the outcome, is likely to affect the tenor of prime-time television. If the FCC is allowed to levy costly fines following slip-ups, television networks say they would be forced to minimize the amount of programming that involves live broadcasting.

A recent federal law increases tenfold the maximum fine the FCC can issue against networks for profanity, to $325,000. Coupled with the FCC’s authority to fine every single affiliate that broadcasts the offending curse word, a single curse could conceivably result in $65 million in fines, lawyers for Fox claim.

The case before the high court stems from lawsuits brought by Fox, CBS, NBC, and ABC in response to findings by the FCC regarding curse words in a variety of programming. In most cases, the FCC has since backed down.

The only case remaining for the Supreme Court to consider is whether Fox Television Stations is liable for expletives aired during the Billboard Music Awards shows in 2002 and 2003. The curses came from the mouths of the entertainers Cher and Nicole Richie. The FCC did not, in the end, fine Fox in either case.

The last time the Supreme Court took up the issue of bad language on the airwaves, it was in response to an extended radio riff by comedian George Carlin in 1973. The monologue, known as the “filthy words” routine, consists of Mr. Carlin’s musings about the “words you couldn’t say on the public airwaves.” The court upheld the FCC’s power to police the airwaves for profanity but left open the question of whether an isolated, passing use of an offensive word counts could result in a fine.

The current Fox case will hinge, in part, on how important the Supreme Court views the government’s interest in protecting children from exposure to profanity. The networks have argued that the rise of cable and satellite television, as well as the Internet, have undermined the FCC’s ability to protect young ears and lessened the need for strict policies against profanity on network TV. The FCC’s rules do not apply to cable or satellite television, or to the Internet, the lawyers argue. Those media, the network lawyers argue, are more likely to expose children to profanity than network television.

“What’s really going on is broadcast networks want there to be no rules at all in the broadcast medium,” the director of public policy at the Parents Television Council, Daniel Isett, said. The council supports the FCC’s stricter policy against curse words.

The FCC’s rules against profanity on network television are in effect between 6 a.m. and 10 p.m.