WASHINGTON - The Supreme Court ruled yesterday that leading someone to believe you have child pornography to show or exchange is a federal crime, brushing aside concerns that the law could apply to mainstream movies that depict adolescent sex, classic literature or even innocent e-mails that describe pictures of grandchildren.

The court, in a 7-2 decision, upheld a law aimed at cracking down on the flourishing online exchange of illicit images of children.

The ruling upheld part of a 2003 law that also prohibits possession of child pornography. It replaced an earlier law the court had struck down as unconstitutional.

The new law sets a five-year mandatory prison term for promoting, or pandering, child pornography. It does not require that someone actually possesses child pornography.

Opponents have said the law could apply to movies like "Traffic" or "Titanic" that depict adolescent sex or the marketing of other material that may not be pornography.

Justice Antonin Scalia, in his opinion for the court, said the law takes a reasonable approach to the issue by applying it to situations where the purveyor of the material believes or wants a listener to believe that he has actual child pornography.

First Amendment protections do not apply to "offers to provide or requests to obtain child pornography," Scalia said.

Likewise, he said, the law does not cover "the sorts of sex scenes found in R-rated movies."

The case came to the Supreme Court after the 11th U.S. Circuit of Appeals struck down the provision in the 2003 law. The Atlanta-based court said it makes a crime out of merely talking about illegal images or possessing innocent material that someone else might believe was pornographic.

In the appeals court's view, the law could apply to an e-mail sent by a grandparent and entitled "Good pics of kids in bed," showing grandchildren dressed in pajamas.

But Scalia said the appeals court interpretation was unreasonable. "The prosecutions would be thrown out at the threshold," he said.

Authorities arrested Michael Williams in an undercover operation aimed at fighting child exploitation on the Internet. A Secret Service agent engaged Williams in an Internet chat room, where they swapped non-pornographic photographs. Williams advertised himself as "Dad of toddler has 'good' pics of her an me for swap of your toddler pics, or live cam."

After the initial photo exchange, Williams allegedly posted seven images of actual minors engaging in sexually explicit conduct. Agents who executed a search warrant found 22 child pornography images on Williams' home computer.

Williams also was convicted of possession of child pornography. That conviction, and the resulting five-year prison term, was not challenged. *