A special panel of three federal judges in Philadelphia will hear final arguments this morning over the constitutionality of the Communications Decency Act, a statute that has become a lightning rod of controversy since its Feb. 8 passage.

The act makes it illegal to knowingly transmit indecent material over the Internet. Opponents challenging the legality of the CDA, which is part of the communications reform bill signed into law on Feb. 8, argue it is too vague and would impose restrictions beyond pornography. Supporters say the restrictions are in line with regulations governing the broadcast industry and do not violate First Amendment guarantees of free speech.

Meanwhile, a voluntary global rating system known as PICS -- for Platform for Internet Content Selection -- yesterday received backing from a consortium of 39 hardware and software companies. Customers who receive PICS software, when it becomes available later this year, will be able to block Internet access to objectionable material.

The computer industry has argued on behalf of a privately developed content ratings system. Moreover, some software companies have indicated plans to build the ratings system directly into their products. CompuServe Inc. officials said yesterday that all of the service's content on the Internet would be compliant with the PICS standard by July. But proponents of the CDA say actions by private industry are not enough to protect minors from sexual and violent material they may run across on the Internet.

The three magistrates who will hear the case today --Dolores Sloviter, the chief judge of the U.S. Third Circuit Court of Appeals, and U.S. District Judges Ronald Buckwalter and Stewart Dalzell -- are expected to make a ruling within the next month. Until then, the CDA has been put on hold.