The Supreme Court on Thursday dismissed sanctions against two television networks that violated the Federal Communications Commission’s ban on vulgar words and nudity, but it sidestepped a more fundamental constitutional question about the government’s power to police the airwaves.

In a unanimous decision, the justices said they need not decide that overarching free-speech question. It was enough, they concluded, to find that the FCC’s 2004 crackdown on even one-time uses of profanity and brief displays of nudity did not give the networks fair notice as to what would violate indecency standards.

Fox was criticized but not fined by the FCC for allowing the broadcast of vulgar words during live award shows before 2004. ABC and local affiliates were fined $1.2 million for showing a 2003 episode of “NYPD Blue” in which an actress’s bare buttocks were displayed for seven seconds in a shower scene.

“The Commission failed to give Fox or ABC fair notice prior to the broadcasts in question that fleeting expletives and momentary nudity could be found actionably indecent,” Justice Anthony M. Kennedy wrote for the court. “Therefore, the commission’s standards as applied to these broadcasts were vague, and the commission’s orders must be set aside.”

The case had raised constitutional questions about whether the FCC should still monitor the nation’s airwaves; the court in 1978 gave the commission the power to regulate the airwaves for indecency during the times children were most likely to be watching, from 6 a.m. to 10 p.m.

The networks had argued successfully in lower courts that those regulations were relics from a time when broadcast television played a significantly different role in American households.

Now, in a world where broadcast networks exist “side by side” with cable channels that are beyond the FCC’s regulation and the Internet is unrestricted, singling out the networks is not only nonsensical but unconstitutional, they argued.

That debate seemed to divide the justices when the case was argued, and the length of time it took to come up with the narrow resolution announced Thursday suggested the court remained knotted.

The case was argued in early January, with Justice Sonia Sotomayor recusing herself. The eight remaining justices may have been evenly split over whether continued regulation by the FCC was warranted or violated the First Amendment.

Only Justice Ruth Bader Ginsburg said, in a concurring opinion, that the court’s 1978 FCC v. Pacifica ruling needed to be reexamined. “Time, technological advances, and the Commission’s untenable rulings in the cases now before the Court show why Pacifica bears reconsideration,” she wrote.

Groups that have urged the FCC to take an even stronger role in monitoring what they say is a coarsening of the broadcast networks were pleased that the commission’s role was not diminished.

“Once again, the Supreme Court has ruled against the networks in their years-long campaign to obliterate broadcast decency standards,” said Tim Winter, president of the Parents Television Council.

“The court today specifically acknowledged the FCC’s ability to continue broadcast-decency enforcement as part of its public-interest obligation.”

But First Amendment specialists said the decision felt more like a reprieve than a resolution.

“The Supreme Court decided to punt,” said Paul Smith, a Washington lawyer who wrote a brief for the National Association of Broadcasters. “The issue will be raised again as broadcasters will continue to try to grapple with the FCC’s vague and inconsistent enforcement regime.”

FCC Chairman Julius Genachowski noted that the decision “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’s directive to protect young TV viewers.”

Fellow commissioner Robert M. McDowell said the FCC must work to “put an end to years of litigation and uncertainty regarding the commission’s regulation of indecent content” and noted that the commission faces a backlog of just under 1.5 million indecency complaints involving 9,700 television broadcasts.

The court said it was also not ruling on the constitutionality of the FCC’s policy. It still contains the prohibition against even fleeting or one-time examples of material that describes or depicts “sexual or excretory organs or activities” and is “patently offensive as measured by contemporary community standards for the broadcast medium.”

Kennedy also wrote that the opinion leaves the FCC “free to modify its current indecency policy in light of its determination of the public interest and applicable legal requirements.”

The networks had argued that the FCC’s rule was arbitrary and unevenly applied; some documentaries and movies that contained curse words and nudity were allowed by the FCC while others were ruled offensive.

The broadcasts at issue in the case included award shows in which Cher told her critics, “F--- ’em,” and Nicole Richie referred to “cow s---” and uttered a variation of the f-word. Complaints generated by parents groups to the FCC resulted in the commission announcing in 2004 that it was changing its policy so that even one-time utterances of profanity could be penalized.

The Supreme Court ruled 5 to 4 in 2009 that the agency was within its rights as a matter of administrative law to change its policy to protect the public against what Justice Antonin Scalia called “foul-mouthed glitteratae from Hollywood.”

But justices sent the case back to the appeals court in New York to determine whether there were constitutional problems with the agency’s actions.

That court agreed that there were. It said the agency’s context-heavy determinations about indecency mean that broadcasters “are left to guess” when profanity and nudity might be deemed appropriate or punishable.The cases are FCC v. Fox Television Stations and FCC v. ABC.

It used the same logic to throw out the finding against ABC, which had resulted in the fine for 40 ABC affiliates that aired the show (including a Texas station owned by a subsidiary of The Washington Post Co.).

Staff writer Sarah Halzack contributed to this report.