Before taking a break, U.S. District Judge Marilyn Hall Patel heard nearly two hours ofarguments in a packed courtroom Wednesday. She has not said when she will rule. Patel expressed concern that 20 million people were logging on to Napster and perhaps that wentbeyond sharing.

“It has an exponential effect,” she said.

The Recording Industry Association of America wants Patel to issue a preliminary injunction to keep San Mateo-based Napster from providing its online service until the matter goes to trial.

Napster users currently trade music over the Internet for free.

The RIAA sued Napster for Napster in December for copyright infringement and related state law violations. The association accused Napster of encouraging users of the company’s software and computer servers to trade copyrighted music online without permission.

Napster had initially responded to the suit by telling the court it was entitled to federalprotections as an Internet service provider, but on May 9, Patel rejected the claim that the DigitalMillennium Copyright Act of 1998 protected it from the illegal actions of its users.

Napster later adjusted its defense strategy, arguing that personal copying of music is protected by federal law.

The dispute between over the free trade of information and the concerns of copyright holders have come to a head in the ongoing battle over Napster. Heavy metal band Metallica has been particularly outspoken against Napster and sued the company for copyright infringement after the band found more than 300,000 users trading their songs online.

In response, Napster blocked access to their service for more than 30,000 of those usersidentified by Metallica, but new users log on daily and continue trading the bands music. It remains unclear whether Internet music file-swapping is so bad for the music industry after all.

A recent study of more than 2,200 online music fans by Jupiter Communications suggests that users of Napster and other music-sharing programs are 45 percent more likely to increase their music purchasing than fans who aren’t trading digital bootlegs online.

“Clearly, people who are using Napster love music. They’re probably our best customers,” saidHilary Rosen, president of the RIAA.

The RIAA estimates that song-swapping via Napster by an estimated 20 million peopleworldwide has cost the music industry more than $300 million in lost sales.

“All of this litigation is really setting the groundwork for what is going to the future of theInternet,” said Larry Iser, an intellectual property attorney.