It is Saturday night and solemn academic study has yielded to casual electronic conversation at the Harvard University computer centre.

Students perched before the glowing rows of terminals, many with their feet up on their desks, explore the endless reaches of the Internet.

Yet an air of unease has hung over this room and hundreds like it since last month's passage of the federal Communications Decency Act, which bans "indecent" words or images from the international computer network.

"Everyone on the Net has a stake in freedom of speech," said Sam Klein, a first-year Harvard student. "Once people start looking over your shoulder, that changes the whole idea."

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The Act, part of a sweeping revision of the United States's telecommunications laws, prohibits "any comment, request, suggestion, proposal, image or other communication that depicts or describes . . . sexual or excretory activities or organs," and any information about abortion. That is more restrictive than the standards used to regulate radio and television broadcasts. There is no specific exemption for material with scientific, literary or artistic merit.

Within minutes of its signing by President Clinton on February 8, the American Civil Liberties Union and 19 other groups successfully filed suit to stop the government from implementing the indecency provision until its constitutionality can be addressed by a federal court in April.

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"This is about the Internet, but it's also about a new level of censorship in the United States under this very vague standard called indecency," said Marjorie Heins, one of the ACLU's attorneys on the case and author of Sex, Sin and Blasphemy: A Guide to America's Censorship Wars. She added that if the ACLU loses and the measure takes effect, such restrictions could grow.

"A big part of the Internet as we know it would come to an end," said David Sobel, co-founder of the Electronic Privacy Information Center, one of the organisations that has filed suit against the government.

Higher education, where the Net is most heavily used, is the major battleground in this debate. Students and faculty have been vocal in their opposition and wore blue ribbons to protest against the passage of the law.

"People in higher education have a special stake in freedom of expression," said Marcia Adler, government relations director for the American Association of University Professors. "Any kind of restrictions on the free flow of ideas is a restriction on academic freedom."

On the other hand, their critics say, some college and university administrators probably secretly welcome the restrictions to absolve them of responsibility for policing cyberspace themselves.

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BREAKDOWN IN COMMUNICATIONS

February 1. Congress approves the final text of the Communications Decency Act.

February 8

President Clinton signs Act and it becomes law. American Civil Liberties Union and others file lawsuit in Federal court in Philadelphia challenging the Act's constitutionality.

February 9

Senators Patrick Leahy and Russell Feingold introduce a Bill to repeal the Act.

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February 15

Judge Ronald Buckwater issues Temporary Restraining Order on the "indecency" provision of the Act. Censorship of "patently offensive" material remains in force.

February 23

Attorney General Janet Reno agreesnot to initiate prosecutions under the "indecency" or "patently offensive" provisions of the Act, pending the conclusion of the litigation. Plaintiffs welcome this as a victory.

February 26

A second lawsuit is filed by a coalition including the American Library Association, Apple and Microsoft, arguing that there are less restrictive means of protecting users fromoffensive material, including in-home filtering software.

March 21

Hearings of evidence of ACLU and co-plaintiffs to begin.

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Documents relating to the Actand the litigation are posted regularly on and