The long-awaited injunction, issued late on Monday, was narrower than record companies had asked for at a hearing on Friday and could give Napster time to launch a service that will pay royalties to artists and record companies.

''Given the parameters we've had in the past, this is much more favorable to Napster than the original injunction was,'' said Eric Scheirer, an analyst with Forrester Research.

A spokeswoman for the Recording Industry Association of America (RIAA) said the group was pleased with the injunction issued by San Francisco District Court Judge Marilyn Hall Patel.

A spokeswoman for Napster said the company's lawyers were studying the injunction.

Patel's ruling went into effect immediately and requires the big music companies suing Napster for copyright infringement to provide lists of the material they wish removed from the system.

The order called for Napster to search for the files within three days of receiving notice of the infringed material.

''Napster is preliminarily enjoined, pursuant to the procedures set forth below, from engaging, or facilitating others in, copying, downloading, uploading, transmitting or distributing copyrighted sound recordings in accordance with this order,'' Patel said.

Patel held a hearing last Friday on how to formulate the injunction and ended the hearing with a promise to draft an injunction order ``that is workable and makes sense.''

''We are gratified the District Court acted so promptly in issuing its injunction requiring Napster to remove infringing works from its system,'' said Hilary Rosen, president of the RIAA.

''We intend to provide the notifications prescribed by the Court expeditiously, and look forward to the end of Napster's infringing activity,'' Rosen said.

The world's biggest record labels -- including Vivendi Universal's Universal Music, Sony Music Warner Music, EMI Group Plc and Bertelsmann AG (BMG) first sued Napster in December 1999, calling it a haven for copyright piracy that would cost them billions of dollars in lost sales.

Patel first issued her injunction against Napster last July but it was held up by an appeals court until February when a three-judge panel largely sided with her decision but asked for modifications.

The case has come to be viewed as the first big battle over copyrights in cyberspace, which will affect how books, movies and other forms of entertainment will be distributed online.

Napster began blocking music files this past weekend in a last-ditch effort to keep the service from being shut down, but users were already figuring out ways to get around the screening mechanism.

Napster's service has attracted about 60 million users who swap songs for free by trading MP3 files, a compression format that turns music on compact discs into small digital files.

Napster was using a filter that takes the names of artists and titles and screens out files that match, but users were figuring out how to outsmart the screening process by finding new ways to identify songs and music files.

Napster users create their own files for songs as they download and trade them.