The embattled music industry -- struggling to halt declining compact-disc sales that it blames on Internet song piracy -- fired another strong counterattack yesterday, suing four college students at three universities who run Napster-like file-sharing sites.

The suits -- filed by the Recording Industry Association of America, the music industry lobby -- ask three U.S. district courts for permanent injunctions to shut down the file-sharing systems that live inside the computer networks at Princeton University, Rensselaer Polytechnic Institute in Troy, N.Y., and Michigan Technological University in Houghton, Mich.

The suits also ask for the highest damages allowable by law, which range up to $150,000 per copyright infringement or, in other words, per pirated song. If awarded, the judgments could run in the millions of dollars.

"We want this infringement stopped for good," said Matthew J. Oppenheim, the RIAA's senior vice president for business and legal affairs. He added that the lawsuits would not be dropped if the file-sharing services were shut down. "Frankly, we are hopeful this round of lawsuits will send a message to others that they should immediately cease and desist."

The four defendants were chosen because the RIAA found their sites to be among the most active, enabling thousands of songs to be freely shared, the RIAA's complaints say. The music industry says such file sharing is in violation of copyright and fair-use laws and takes money away from artists and record companies.

The RIAA has sued Web sites and individuals in the past -- some of whom were students -- but this is the first time the organization has leveled such legal firepower at students using college networks.

Of the four defendants, only Aaron Sherman of Rensselaer would confirm he is being sued, and he declined further comment. The others declined comment or could not be reached.

The RIAA suits allege that the four defendants offered between 27,000 and 1 million songs each for free trading.

As of yesterday afternoon, Oppenheim said, three of the four sites had shut down.

"This is a particularly flagrant way to illegally distribute millions of copyrighted works over the Internet," said RIAA President Cary H. Sherman. "The people who run these Napster networks know full well what they are doing -- operating a sophisticated network designed to enable widespread music thievery."

The RIAA employs software that scours the Internet looking for what it believes are illegally traded songs. But the networks named in the lawsuits are internal college networks, known as local area networks, or LANs, and are not seen by the RIAA software.

Instead, the RIAA discovered them by reading college newspapers, in which the LANs are discussed. Several Princeton sites were listed in a November article in the Daily Princetonian, which also included a statement from the school's information technology department saying that it is against university regulations to use the Internet to violate copyright laws.

After that, Oppenheim said, it was easy to identify whom to sue.

"These people are not shy," he said. "I believe their names were on their Web sites."

At Princeton, the Web site being targeted is Wake.Princeton.edu, a file-sharing system that connects one student's public files with those of other students on the system.

For instance, if a student wanted to download the new Linkin Park single, the student would type the song's title into Wake, which acts like a search engine, and it would display other students' computers where that song file resided. The student could then download the song by clicking on a link.

The RIAA could have gone through Princeton's administrative process and filed a complaint against the student running the Wake site, said Lauren Robinson-Brown, director of communications at Princeton.

"They are well aware of that procedure," she said. "They regularly file with us."

The music industry has blamed free peer-to-peer music file sharing for its current depression, as sales of compact discs have dropped dramatically over the past few years. Advocates of file sharing say that the music industry caused the creation of systems such as Napster -- which was shut down by court order in 2001, an effort led by the RIAA -- by pricing CDs near $20.

Further, say analysts, the music industry has been slow to adapt to the changing patterns of music consumers, many of whom want their music on a song-by-song basis as opposed to buying an entire CD.

Among the record companies represented by the RIAA are Universal Music Group, the industry's largest, owned by Vivendi Universal; AOL Time Warner Inc.'s Warner Music Group; and Sony Music Entertainment.

The music industry has fought back against file sharing through the courts and by creating its own online music services, such as MusicNet and Pressplay, through which consumers can use their computers to buy or rent music, some of which they can download and burn onto CDs.