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The Supreme Court ruled Tuesday that a law meant to punish pornographers who peddle dirty pictures to Web-surfing kids is probably an unconstitutional muzzle on free speech.

The high court divided 5-to-4 over a law passed in 1998, signed by then-President Clinton and now backed by the Bush administration. The majority said a lower court was correct to block the law from taking effect because it likely violates the First Amendment.

In considering the issue a third time, the court did not end a long fight, however. The majority voted to send the case back to a lower court for a trial that could give the government a chance to prove the law does not go too far.

The ruling in Ashcroft v. American Civil Liberties Union (search) was the last of nearly 80 cases decided in a busy court term that ended Tuesday with no announcements that any of the nine justices would retire.

The year's marquee cases involving presidential power to deal with suspected terrorists were announced Monday, and for the most part represented a loss for the Bush administration.

The majority, led by Justice Anthony M. Kennedy (search), said there may have been important technological advances in the five years since a federal judge blocked the law.

Holding a new trial will allow discussion of what technology, if any, might allow adults to see and buy material that is legal for them while keeping that material out of the hands of children.

Justices John Paul Stevens, David H. Souter, Clarence Thomas and Ruth Bader Ginsburg agreed with Kennedy.

Tuesday's pornography ruling is more nuanced, but still a blow to the government. It marks the third time the high court has considered the case, and it may not be the last.

The ACLU and other critics of the antipornography law said that it would restrict far too much material that adults may legally see and buy.

"We're very pleased with the decision," ACLU lawyer Ann Beeson said. "The status quo is still with us and the court made it safe for artists, sex educators and Web publishers to communicate with adults without risking jail time."

Beeson said that after repeated losses in court, the government may choose to drop any further defense of the law. There was no immediate word from the Bush administration.

The law, which never took effect, would have authorized fines up to $50,000 for the crime of placing material that is "harmful to minors" within the easy reach of children on the Internet.

The law also would have required adults to use access codes and or other ways of registering before they could see objectionable material online.

For now, the law, known as the Child Online Protection Act (search), would sweep with too broad a brush, Kennedy wrote. "There is a potential for extraordinary harm and a serious chill upon protected speech" if the law took effect, he said.

Kennedy said that filtering software "is not a perfect solution to the problem of children gaining access to harmful-to-minors materials." So far, he added, the government has failed to prove that other technologies would work better.

In dissent, Chief Justice William H. Rehnquist and justices Sandra Day O'Connor, Antonin Scalia and Stephen Breyer said the law is constitutional and should be upheld.

Restrictions about who would be covered by the law and how it would be enforced "answer many of the concerns raised by those who attack its constitutionality," Breyer wrote.

Congress had tried repeatedly to find a way to protect Web-surfing children from smut without running afoul of the First Amendment.

The justices unanimously struck down the first version of a child-protection law passed in 1996, just as the Internet was becoming a commonplace means of communication, research and entertainment.

Congress responded by passing COPA, saying the new law met the Supreme Court's free-speech standards.

The ACLU challenged COPA immediately, arguing that the replacement law was every bit as unconstitutional as the original. The law has been tied up in the courts ever since.

The ACLU challenged the law on behalf of online bookstores, artists and others, including operators of Web sites that offer explicit how-to sex advice or health information. The ACLU argued that its clients could face jail time or fines for distributing information that, while racy or graphic, is perfectly legal for adult eyes and ears.

Material that is indecent but not obscene is protected by the First Amendment. Adults may see or purchase it, but children may not.

A Philadelphia-based federal appeals court has stuck down the law twice, on both broad and fairly narrow grounds.

The case is Ashcroft v. ACLU, 03-218.