The U.S. Department of Justice has said it will not enforce the law until the court challenge is resolved.
Opponents of the act favor parental oversight and voluntary rating of Internet content. In court they have contended that the law is vague and over-broad and could prohibit frank online talk about AIDS, selections from Shakespeare and the Bible, legitimate artwork and uncensored library catalogs.
An official from America Online has said the service could not effectively comply with the law and might have to dump its ``chat'' areas if the company was liable for dirty words typed in by members.
Supporters say those challenging the law are whipping up hysteria with such talk, that its focus is much more narrow, and that it merely extends to a new medium restrictions already in place for broadcasting and the dial-a-porn industry.
Whichever way the panel of judges in Philadelphia rules, the case is headed for an appeal to the U.S. Supreme Court, both sides have said. A similar case being heard by a federal court panel in Manhattan and scheduled for final arguments on June 3 could also be consolidated with the Philadelphia case when it reaches the high court.
Supporters of the law - conservative religious, family-values and anti-pornography groups - say it is needed to stem a tide of online pornography. Without it, ``we leave the Internet the way it is, which is unregulated and dangerous and off-limits to kids,'' said Bruce Taylor, president of the anti-pornography National Law Center for Children and Families.
Taylor helped write the Communications Decency Act and has filed an 83-page legal brief backing the government.
The opponents - a coalition of rights organizations, publishers and computer industry groups - say the act criminalizes speech that is protected by the First Amendment in print and other media, and reduces the level of all online discourse to that acceptable for young children.
In five days of testimony since March, the plaintiffs demonstrated that a broad range of software programs, with names like SurfWatch and Cyber Patrol, are already available - and more are in the pipeline - to allow parents and educators to filter undesirable material from the Internet before it reaches the computer screens of children.
On that score just yesterday, a consortium of computer firms announced that a voluntary global rating system known as PICS - for Platform for Internet Content Selection - had been in the works for nearly a year.
Thirty-nine Internet-related firms, including America Online, CompuServe, Microsoft, Prodigy and Netscape Communications, said that in the coming months they would give customers PICS software to block access to objectionable sexual and violent material.
The Philadelphia case is being heard by Dolores K. Sloviter, chief judge of the U.S. Third Circuit Cort of Appeals, and U.S. District Judges Ronald L. Buckwalter and Stewart Dalzell. They are expected to issue a ruling in the next few weeks. The law is on hold pending the outcome of legal challenges.