Broadcasters had argued that the revolution in technology that brought the Internet, satellite television, and cable has made the rules obsolete. The regulations apply only to broadcast channels.
The justices said the FCC is free to revise its indecency policy, which is intended to keep the airwaves free of objectionable material during the hours when children are likely to be watching.
The agency's chairman, Julius Genachowski, said the ruling "appears to be narrowly limited to procedural issues related to actions taken a number of years ago. Consistent with vital First Amendment principles, the FCC will carry out Congress' directive to protect young TV viewers."
It was the second time the court has confronted but not ruled conclusively on the FCC's policy on isolated expletives. Justice Anthony Kennedy said in his opinion for the court that "it is unnecessary for the court to address the constitutionality of the current policy."
The narrow decision, coupled with the more than five months that elapsed between the argument in January and Thursday's decision, could mean that the justices struggled and failed to reach agreement on a broader outcome.
Broadcasters argue that viewers now have many options, unlike the handful of channels they had available in the 1960s and 1970s when the court last weighed in on indecency on the airwaves. In many cases, viewers don't even know when they are switching between the older broadcast channels and cable.
Still, the regulated broadcast channels provide what the government has called a safe haven of milder programming, and those channels remain dominant, even in the Internet age, the administration argued.
Paul Smith, a First Amendment expert and partner with the Jenner & Block law firm in Washington, said the court should expect more challenges until it rules definitively.
"The Supreme Court decided to punt on the opportunity to issue a broad ruling on the constitutionality of the FCC indecency policy. The issue will be raised again as broadcasters will continue to try to grapple with the FCC's vague and inconsistent enforcement regime," said Smith, who wrote a brief supporting the broadcasters.
The case arose from a change in the FCC's long-standing policy on curse words.
For many years, the agency did not take action against broadcasters for one-time uses of curse words. But after several awards shows with cursing celebrities in 2002 and 2003, the FCC toughened its policy after it concluded that a one-free-expletive rule did not make sense in the context of keeping televison free of indecency when children are likely to be watching.
But Kennedy, in the ruling throwing out the fines, said the commission did not adequately explain that under the new policy "a fleeting expletive or a brief shot of nudity could be actionably indecent."
The stepped-up indecency enforcement, which included issuing record fines for violations, also was spurred in part by widespread outrage following Janet Jackson's breast-baring performance during the 2004 Super Bowl halftime show on CBS.
That incident and the FCC's proposed fine of $550,000 were not part of the current case. The government has an appeal pending of a lower court ruling that threw out the fine in that case.