The unanimous high court ruling, written by Justice Anthony Kennedy, declared that the FCC's standards were vague as applied to the broadcasts at issue in the case. It did not decide the larger question of whether the indecency policy violated constitutional free-speech rights.

Under the policy which dated to 2001 and was amended in 2004, broadcasters can be fined for airing a single profanity blurted out on a live show or for brief nudity. Government lawyers said it covered the "F-word" and the "S-word" that denote "sexual or excretory activities," respectively.

The justices threw out a U.S. appeals court ruling that struck down the policy on speech grounds and the justices said several options are before the commission, including reviewing the current policy and modifying it.

FCC Chairman Julius Genachowski said the agency is reviewing the Supreme Court decision, which he said appeared narrowly limited to procedural issues over actions taken years ago.

"Consistent with vital First Amendment principles, the FCC will carry out Congress's directive to protect young TV viewers," Genachowski said in a statement.

Republican Commissioner Robert McDowell said the agency should quickly implement the Court's decision and move on to address a backlog of nearly 1.5 million pending indecency complaints, dating as far back as 2003 and involving some 9,700 TV broadcasts.

"We owe it to the American public and the broadcast licensees involved to carry out our statutory duties with all deliberate speed," he said.

The case involved 2002 and 2003 awards shows on News Corp's Fox television network when singer Cher blurted out an expletive and actress Nicole Richie used two expletives. The FCC said the network violated its indecency rules.

The case also involved a seven-second shot of a woman's nude buttocks on a 2003 "NYPD Blue" episode on Walt Disney Co's ABC network that led to $1.21 million in fines.

The FCC already had launched its indecency crackdown when pop star Janet Jackson briefly exposed her breast during a 2004 broadcast of a halftime show for the Super Bowl football game, drawing half a million complaints.

Kennedy in the ruling based the decision on the constitutional due process requirement, saying that broadcasters had to be given fair notice of the policy and the restrictions.

"A fundamental principle in our legal system is that laws which regulate persons or entities must give fair notice of conduct that is forbidden or required," he wrote in the 18-page opinion.

He said there was no need to address the constitutional free-speech issue under the First Amendment.

The FCC can impose fines of $325,000 on each station that airs indecent material, including images and words, between 6 a.m. and 10 p.m.

Critics including the broadcast industry said the policy had been applied inconsistently, with the FCC allowing the television broadcast of profanity in the World War Two movie "Saving Private Ryan" and of nudity in the movie "Schindler's List."

"NAB has long believed that responsible industry self-regulation is preferable to government regulation in areas of programming content," said Dennis Wharton, executive vice president of communications at the National Association of Broadcasters.

The FCC policy applies only to broadcast television and radio. Neither cable nor satellite channels are subject to FCC content regulation.

Wharton said viewers can continue to expect broadcast programming to be less explicit than pay-TV offerings despite the ruling in their favor.

The Supreme Court ruled in 2009 on narrower grounds that the FCC's indecency policy was a rational and legally permissible use of the FCC's administrative powers, but did not reach the free-speech issue at that time.

In the cases decided Thursday, the networks also had asked the high court to overturn its 1978 ruling that upheld the FCC's power to regulate indecency in a case about comedian George Carlin's "Filthy Words" monologue on radio, arguing the media landscape had changed dramatically.

In the main opinion by Kennedy, the court did not address that ruling.

But Justice Ruth Bader Ginsburg, with Justice Clarence Thomas concurring, issued a one-paragraph opinion saying the 1978 decision was wrong when it was issued.

"Time, technological advances and the commission's untenable rulings in the cases now before the court show why" the 1978 ruling should be reconsidered, Ginsburg wrote.

Justice Sonia Sotomayor did not take part in the latest ruling. She considered the dispute previously as a U.S. appeals court judge in New York.

The Supreme Court case is FCC v. Fox Television Stations and FCC v. ABC Inc, No. 10-1293.

(Reporting By James Vicini; Additional reporting by Jasmin Melvin; Editing by Jackie Frank and Vicki Allen)

• A Permanent Economic Emergency