PHILADELPHIA (AP) _ A panel of federal judges blocked enforcement of a new law barring ``indecent'' material on the Internet, saying the worldwide computer network is protected by the First Amendment guarantee of free speech.

In trying to make sense of the free-for-all world of the Internet, a unique three-judge panel granted a preliminary injunction against the Communications Decency Act while two lawsuits wind through the court system.

The decision, the first major judicial ruling on the Internet, was anxiously awaited by the government and the 57 groups challenging the act. The government has promised to appeal, taking the case directly to the U.S. Supreme Court for review.

``Just as the strength of the Internet is chaos, so the strength of our liberty depends upon the chaos and cacophony of the unfettered speech the First Amendment protects,'' the judges wrote.

Only the judges' ruling on the preliminary injunction holds the force of law, but their logic gives the first glimpse of how the federal judiciary will view the Internet.

Betty Turock, president of the American Library Association, one of the groups that brought the legal action, hailed the ruling as ``a victory for librarians, everyone who uses libraries and and everyone who believes in free speech.''

The act, enacted Feb. 8 as part of a behemoth overhaul of telecommunications legislation, makes displaying ``indecent'' or ``patently offensive'' words or images on the Internet punishable by $250,000 fines and a two-year prison sentence if they are accessible to minors.

With child pornography already illegal, the law was designed to keep nude pictures of adults off screens available to children. But the judges said the effort was impotent, noting that, for one thing, much Internet material comes from overseas.

A key issue addressed by the judges was whether to extend the First Amendment rights enjoyed by the print media to the Internet, or to let it be regulated as broadcasters are. The judges granted ``at least as much protection'' as print.

``As the most participatory form of mass speech yet developed, the Internet deserves the highest protection from governmental intrusion,'' the judges wrote.

The judges said any effort to stifle the unique medium would violate the Constitution.

``The Internet is a far more speech-enhancing medium than print,'' the judges said. ``Because it would necessarily affect the Internet itself, the CDA would necessarily reduce the speech available for adults on the medium. This is a constitutionally intolerable result.''

Opponents had argued that the Internet should be classified as print media, which the courts have given wide latitude, reasoning that adults can provide their own censorship by merely declining to buy a publication.

The government, noting that Internet images flow on telecommunication lines, argued that it fits the definition of the broadcast media. Courts have allowed limitations on broadcast speech, saying technology restricts the number of stations and they are easily accessible to children.

The order also prohibits the government from enforcing a provision restricting speech about abortion on computer networks. But President Clinton, when he signed the law, said the Justice Department would never bring charges under the clause because a long line of Supreme Court decisions already had outlawed the restrictions.

In the only precursor to the decision, one of the three judges issued a temporary restraining order Feb. 15 that blocked part of the law, declaring the term ``indecent'' too vague.

The judge left the government free to prosecute the ``patently offensive'' provisions, defined as online communication that ``in context, depicts or describes in terms patently offensive as measured by contemporary community standards, sexual or excretory activities or organs.''

Although both sides found the decision confusing, Justice Department officials decided not to begin prosecuting violators until the case is decided.

The panel issuing today's ruling consists of Dolores K. Sloviter, chief judge of the 3rd U.S. Circuit Court of Appeals, and U.S. District Judges Ronald L. Buckwalter and Stewart Dalzell.

The law itself specified that an appeals judge and two federal district judges would review the law, and that if the government lost, the case would go directly to the Supreme Court.