A Supreme Court debate about Congress' ability to regulate the shadowy world of computer-simulated child pornography became a real-world discussion of the sex scenes in modern movies Tuesday during a lively argument session over free speech, art and kiddie porn.

Does the movie Traffic appear to show adolescents having sex? the justices asked. Under a 1996 law challenged by pornographers and free-speech advocates, could someone be prosecuted for buying a video copy of that movie, or the films Lolita, or Titanic?

All three movies include bedroom scenes of teen-agers or young adults, though their private parts are obscured.

The 1996 law at issue in Tuesday's case forbids any visual depiction that "appears to be" children in sexually explicit situations, or that is advertised so that it "conveys the impression" that someone under 18 is involved.

Through high-tech wizardry or simple deception, pornographers can make dirty movies that appear to show kids having sex, but which actually involve no real children.

The Supreme Court must decide if it violates the First Amendment for government to ban something that appears to be one thing but is really another.

"I don't know whether they depict simulated sexual activity or not. I didn't see any of those movies," Justice Antonin Scalia interjected after about 10 minutes of movie discussion.

The court heard arguments in a borrowed courtroom for a second day Tuesday because of anthrax contamination at the Supreme Court building. Chief Justice William Rehnquist said the court will also be displaced Wednesday.

In Tuesday's case, the Justice Department is asking the Supreme Court to uphold the Child Pornography Prevention Act provisions in part to help "stamp out the market for child pornography involving real children."

Constitutional free-speech rights do not fully extend to pornography, and the Supreme Court has ruled that child pornography gets even less protection. The First Amendment does not apply because the "evil to be restricted so overwhelmingly outweighs the expressive interests, if any, at stake," the court ruled in 1982.

Outright use of children to depict sex acts is illegal, as is possession or transmission of illicit child porn.

Savvy pornographers have long fooled the eye with adults who look very young. Their options expanded with the advent of sophisticated computer programs that allow people to alter photos or create entirely fake images.

The Free Speech Coalition, the California-based trade association involved in this case, says it opposes child pornography but worries that the 1996 law would sweep up even law-abiding pornographers.

"The very crux of the matter is that even reasonable people may differ on what 'appears to be' a minor and what 'conveys the impression' that a minor is depicted," the pornographers' group argued in legal filings with the court.

The group did not challenge a section of the law that banned the computer doctoring of pictures of real and sometimes identifiable children to appear sexually explicit.

A federal judge upheld the law, but the 9th U.S. Circuit Court of Appeals reversed that decision in 1999, ruling that the government did not show a connection between computer-generated child pornography and the exploitation of actual children.

Several other appeals courts have ruled the opposite way, and the government asked the high court to resolve the differences.

The Justice Department argues that fake images could be used to entice real children into sexual activity.

"Congress regarded the material covered by the CPPA as a tool of the crime of child abuse much like burglars' tools are instruments of the crime of burglary," Solicitor General Theodore Olson wrote in legal filings with the court.

The government also argued that unless all child porn is banned it may be impossible for investigators to tell what is real, illegal porn.

Thirty-six states and territories joined the National Center for Missing and Exploited Children, 18 members of Congress and conservative groups such as the Family Research Council in filing friend-of-the-court briefs supporting the government in the child pornography case.

The American Civil Liberties Union, other civil liberties groups and criminal defense lawyers joined media groups and publishers in backing the pornographers.

The case is Ashcroft v. Free Speech Coalition, 00-795.