In defending itself against the legal onslaught of the recording industry, the controversial MP3 music distributor Napster arguing that it is simply an Internet service provider.

In compliance with the "notice and take down" provision of the Digital Millennium Copyright Act of 1998, Napster has blocked the passwords of more than 300,000 of its users alleged to have swapped songs by the rock band Metallica.

Metallica demanded that the users be removed from the system last week, when it delivered to Napster's offices 13 boxes of documents listing the user names of people who allegedly violated the band's copyrights.

"Napster has taken extraordinary steps to comply with Metallica's demands," Napster attorney Laurence Pulgram says in a statement. "Napster has always stated that it would act in response to notice from copyright holders, and it has lived up to that commitment in good faith."

The move bolsters Napster's claim that it should be treated like an ISP in the eyes of the law. ISPs are not held responsible for illegal content flowing across their networks, but if they are notified of a case of alleged infringement, they are required to act.

Metallica could sue individual Napster users personally if they continue to trade copyrighted songs after being notified.

However, the band is unlikely to take this step. "Metallica is not going to sue its fans, no matter how delighted Napster would be to see that," says Metallica attorney Howard King.