By Andy Sullivan

WASHINGTON (Reuters) - U.S. lawmakers have asked Attorney General John Ashcroft to go after Internet users who download unauthorized songs and other copyrighted material, raising the possibility of jail time for digital-music fans.

In a July 25 letter released late Thursday, some 19 lawmakers from both sides of the aisle asked Ashcroft to prosecute "peer-to-peer" networks like Kazaa and Morpheus and the users who swap digital songs, video clips and other files without permission from artists or their record labels.

The Justice Department should also devote more resources to policing online copyrights, the lawmakers said in their letter.

"Such an effort is increasingly important as online theft of our nation's creative works is a growing threat to our culture and economy," the letter said.

A Justice Department spokesman declined to comment.

The recording industry says peer-to-peer services cut into CD sales, and has been battling them in court since 1999, when the five major labels sued pioneer service Napster Inc.

A U.S. federal judge ordered Napster to shut down its service in July 2001, but upstarts like Kazaa and Morpheus soon took its place. Kazaa, which in addition to music allows users to swap movies and other media files, said this week that its free software had been downloaded 100 million times.

Music labels have not ruled out suing individual users, and have pushed for the right to flood peer-to-peer networks with bogus files, or disrupt them by other means.

While a debate has raged on Capitol Hill over the proper balance between copyright and technological innovation, U.S. law-enforcement authorities have taken a minimal role.

The Justice Department filed a supporting motion siding with the record labels in the Napster case, but has brought no cases of its own.

The move was welcomed by the Recording Industry Association of America, which represents the five major labels --Bertelsmann AG BTGGga.D , Vivendi Universal EAUG.PA , Sony Corp 6758.T ., AOL Time Warner Inc AOL.N . and EMI Group Plc EMI.L .

"There is no doubt, mass copying off the Internet is illegal and deserves to be a high priority for the Department of Justice," said RIAA Chairman Hilary Rosen in a statement.

An analyst for a digital civil-liberties group said the Justice Department probably had better things to do with its time.

The letter "implies that Justice should be going after relatively innocent behaviors that I suspect most Americans don't think warrant the time," said Alan Davidson, an associate director at the Center for Democracy and Technology.

On the other hand, "we would much rather see current authorities be used before Congress goes and creates brand new laws," Davidson said.

A staffer for Texas Republican Rep. Lamar Smith, who signed the letter, said that lawmakers did not want FBI agents to arrest casual users but instead go after operators of network "nodes" that handle much of the traffic.

Among those signing the letter were: Delaware Democratic Sen. Joseph Biden; Wisconsin Republican Rep. James Sensenbrenner; Virginia Democratic Rep. Bobby Scott; Michigan Democratic Rep. John Conyers; North Carolina Republican Rep. Howard Coble; and California Democratic Sen. Dianne Feinstein.