Central Washington University and one other college are experimenting with a controversial network filter that can identify and automatically cancel the transfer of copyrighted songs. The two colleges are apparently the first to try the technique, which has been endorsed by record companies but criticized by privacy advocates.

Vance Ikezoye, chief executive of Audible Magic, which sells the filter, said the other college had asked not to be named. Audible Magic also markets the product, called the CopySense Network Appliance, to nonacademic customers, including businesses and government agencies.

Invisible to users, the device essentially scans song files traded on a campus network, hunting for digital fingerprints that match those in a database of four million copyright-protected songs. If the device finds a match, it stops the file transfer, and the campus user gets a notice saying that the connection was lost.

The filter has recently been promoted by the Recording Industry Association of America as a new technology with the potential to end illegal file trading without blocking other Internet traffic. Last month the company helped set up demonstrations of the technology for members of Congress and for college leaders. Company officials say each device costs between $15,000 and $40,000, depending on the speed of the institution's Internet connection.

Chris Timmons, a network engineer at Central Washington, said the university had been testing the device on its residence-hall network for two months. He does not yet have a firm estimate of how many trades have been blocked, he said, or of how much faster the network is now that traffic is filtered, but he said the university was likely to purchase the product. "It's already becoming something we rely on," he said.

He said his staff had spent "a lot of time" responding to cease-and-desist orders from copyright owners, who often alert network officials about individual instances of illegal file trading. He hopes the device will greatly reduce those notices.

"Practically every university has an acceptable-use policy against trading copyrighted works," he said. "But there really wasn't a tool that you could put out there to help you enforce that."

Like many universities, Central Washington already uses a tool, called a bandwidth shaper, that limits the amount of bandwidth available for trading files so that song-swapping doesn't overwhelm the network. But Mr. Timmons said that many users had figured out ways to circumvent the bandwidth shaper.

Although Mr. Timmons said he thinks of himself as a "privacy advocate," he said the filter was necessary because music piracy "is illegal and it violates our acceptable-use policy."

"Professionally, I can't turn the other cheek on that," he said.

"We are proceeding cautiously with respect to tools such as the CopySense Appliance," he added. "It is important to us that the scope of what the appliance looks for includes only the digital signatures of copyright-protected works."

But some privacy advocates object strongly to the new filter.

"That's a level of surveillance that I think is just completely unacceptable," said Fred von Lohmann, a lawyer with the Electronic Frontier Foundation, which has opposed the recording industry in file-sharing debates and in court. "If we searched every house in America, we could find out more evidence about who the bad guys are, but we don't tolerate that."

Mr. Ikezoye, of Audible Magic, said the filter did not violate privacy because the software can be set so that it does not keep a record of who is trading songs. "We don't care who is doing the transfer -- uploading or downloading," he said. "We just stop the transfers as they take place." He said the company would soon release a version of the software for colleges that would make it impossible for network administrators to identify file traders.

Mr. Ikezoye compared his company's product to software that scans computer networks for viruses and automatically deletes them, a technique that is in use on many campuses. That analogy is attractive to many in academe who are struggling with managing their campus networks.

"That was the thing that really caught my attention," said Charles Phelps, provost of the University of Rochester, who had the company demonstrate the software to his staff. "We're doing that all the time to protect ourselves from viruses."

Mr. Phelps is a member of the Joint Committee of the Higher Education and Entertainment Communities, led by Graham B. Spanier, president of Pennsylvania State University at University Park. The group is trying to help colleges find ways to manage the problem of illegal file sharing.

Mr. Phelps said that Rochester was not ready to buy the filter yet because he still has questions about how much faster it will make the network. His biggest question is whether the filter will catch enough to make it worthwhile, since it can only block transfer of the songs in its database. Movies and other large files can still be traded unless campus officials simply set the device to block all file trading, which many are reluctant to do because they do not want to stop legitimate uses of the technology.

"For the first time," Mr. Phelps said, "I'm actually having students complain to me, 'The network is so slow. Can't you do something about this illegal file sharing?'"

Other campus-computing experts argue that scanning music files based on content is very different from eliminating viruses.

"Viruses are a clearly identifiable and recognized threat to the network," said Tracy Mitrano, policy adviser to the Office of Information Technologies at Cornell University. "The question of content is a separate issue from security."

She said she had not seen a demonstration of the Audible Magic filter, but was concerned that it might violate a university policy that protects network users' privacy.

Last year Audible Magic conducted a test of its system at the University of Wyoming and issued a news release that attracted media attention. But Robert Aylward, vice president and chief information officer at the university, said in an interview last week that the university no longer used the system, and had never used its filtering feature because Wyoming officials did not want to monitor traffic. Instead, he said, they set the device to function as a bandwidth shaper.

"We've never had the discussion at this university about monitoring content," said Mr. Aylward. "And we have some very serious concerns about monitoring any content."

"We've disconnected the Audible Magic and returned it," he added.

Some campus officials argue that no filter or other technology will solve the music-piracy problem.

"I don't think it's a technology problem -- it's a cultural and education problem," said John E. Kolb, chief information officer at Rensselaer Polytechnic Institute, who recently saw a demonstration of the technology. Filters alone "are never going to be a complete solution because people will figure out a way to beat the system."

In fact, file traders could beat the Audible Magic system if they compressed or encrypted their music files before they traded them, company officials acknowledged. The officials added, however, that they would be able to update their software to detect compressed files if that began to happen.

"An arms race is what it will be become," said Mr. Ikezoye.