The U.S. Supreme Court has stepped into one of the biggest free speech fights of the past three decades, but it's unclear how far the court will go when it rules on just how much trouble broadcasters can get into for a slip of the tongue.

On Monday, the court agreed to hear arguments over the Federal Communications Commission's policy regarding so-called "fleeting expletives" in a closely watched case that will decide whether the government can fine or revoke a broadcaster's license because someone says a bad word. The case will be argued late this year.

Both News Corp., the Fox Broadcasting parent that wanted its victory in a lower court to stand, and the FCC, which pushed the Bush administration to appeal the case, applauded the justices' decision.

"The commission, Congress and most importantly parents understand that protecting our children is our greatest responsibility," FCC chairman Kevin Martin said.

Solicitor general Paul Clement, the Bush administration's top lawyer, urged the court to take the case, arguing that the appeals court decision had placed "the commission in an untenable position," powerless to stop the airing of expletives even when children are watching.

Fox said the move would "give us the opportunity to argue that the FCC's expanded enforcement of the indecency law is unconstitutional in today's diverse media marketplace, where parents have access to a variety of tools to monitor their children's television viewing."

The case surrounds two incidents in which celebrities used profanity during the Billboard Music Awards. In 2002, Cher told the audience: "People have been telling me I'm on the way out every year? So f--- 'em." The next year, Nicole Richie said: "Have you ever tried to get cow s--- out of a Prada purse? It's not so f---ing simple." (The Nielsen Co. owns Adweek and Billboard.)

Although the case concerns those utterances, it is grounded in a policy the commission developed after a 2004 incident in which U2's Bono said on NBC that winning a Golden Globe was "really, really f---ing brilliant." After that, the commission changed its long-standing policy and decided that some words are so inherently awful that broadcasters are liable even if the words come as a surprise. (NBC challenged the decision, but that case has yet to be resolved.)

The FCC found that Fox violated the Bono doctrine for the comments made by Cher and Richie, but the panel decided against issuing a fine because the shows aired before the commission altered the policy.

Fox, CBS, NBC and other broadcasters challenged the commission's decision, arguing that it chills free speech, threatens live programming and is unduly vague.