Top Senate leaders from both parties launched an assault on online music and video file-sharing services yesterday, introducing legislation that makes anyone who "induces" illegal copying just as liable for breaking copyright law as someone who makes the copies.

The proposed law, backed by Majority Leader Sen. Bill Frist (R-Tenn.) and Minority Leader Sen. Thomas A. Daschle (D-S.D.), is intended to crack down on the free file-sharing services that the recording and movie industries claim are costing them millions of dollars in lost sales.

But some legal experts argue that the bill is worded so broadly that it threatens numerous electronic devices and software products that enable copying of digital entertainment. And opponents worry that the bill is being hustled through the Senate without sufficient hearings and debate.

File-sharing software allows users to trade music, video and other software files. Kazaa, the largest of the networks, claims more than 30 million users who have downloaded more than 1 billion files.

Although music companies have sued more than 3,000 people who use file-sharing software, the entertainment industry has so far failed to convince judges that services such as Kazaa, Grokster or Morpheus should also be held responsible.

Instead, in a key ruling late last year, a federal court in California said that as with copying machines or other devices, the fact that some consumers use file sharing for illegal purposes does not mean the networks themselves are liable.

The bill will be taken up by the Judiciary Committee, headed by Sen. Orrin Hatch (R-Utah), who is the legislation's chief sponsor. Hatch said the legislation is partly in response to the California decision, which the entertainment industry has appealed.

"Unfortunately, the court which found that adults now profit by inducing children to commit illegal and criminal acts also demanded 'additional legislative guidance' about whether the artists harmed by this scheme can sue its architects instead of the children swept into its clutches," Hatch said.

Proponents, including Sen. Patrick J. Leahy of Vermont, the ranking Democrat on the committee, said the measure was narrowly crafted to go after only those deliberately aiding illegal copying, not any particular technology.

But several copyright experts said the bill could have a chilling effect on anyone who makes copying technology.

"I find it sort of scary," said Jessica D. Litman, a law professor at Wayne State University. "It is worded so broadly that it . . . threatens to sweep within it all of the other activities, devices and technologies that have infringing as well as non-infringing uses." These might include, for example, machines that "burn" compact discs or digital video discs (DVDs).

Litman said the California decision rested on an earlier U.S. Supreme Court decision on videocassette recording technology that found that if a device has a "substantial" legal use, its makers cannot be held liable for how people use it.

"This is something else," she said. "It's a new kind of third-party liability for people who wouldn't be liable" under current law.

Under the bill, someone would be liable if he or she intentionally "aids, abets, induces or procures" illegal material. Intent is defined as what a reasonable person would determine based on "all relevant information about such acts . . . including whether the activity relies on infringement for its commercial viability."

Susan P. Crawford, a professor of Internet law at the Benjamin N. Cardozo School of Law in New York, said that any lawyer advising makers of devices, software or even Internet service providers would be compelled to warn them that they could face secondary liability if they know their products might get used for illegal purposes.

"The VCR would not be a legal product; TiVo would not be a legal product," said Gary Shapiro, president of the Consumer Electronics Association. "I'm surprised the leadership would jump on this bill without hearing from the other side."

The copyright community, including the Business Software Alliance, which is heavily funded by Microsoft Corp., cheered the bill and said it has no desire to hurt electronics or software makers.

"Enabling technologies have nothing to worry about as long as they are not inducing other people to violate the copyright law," said David Green, a vice president of the Motion Picture Association of America.

Green and other proponents of the bill say they recognize that even file-sharing networks have legitimate uses -- such as providing Internet phone service -- and that only those who promote illegal activity would be liable.

"We have a huge piracy problem," said Emery Simon, of the Business Software Alliance. "Current law makes it difficult" to go after all the infractions.

Opponents of the bill, and some in the technology industry who have not yet declared their allegiances, say they are taken aback by the fast track the bill seems to be on.

"The legislation seems vague at best, potentially overbroad and perhaps even chilling towards innovation," said Bruce P. Mehlman, a former assistant commerce secretary for technology who left the Bush administration last year to head a trade association of computer makers. "With the potential for unintended consequences so high, one would at least hope for hearings and debate."

Philip S. Corwin, an attorney for the owners of Kazaa, called the process "shocking and shameful."

"We and other congressional committees have had numerous hearings on this issue and we may well schedule more in the future if the chairman thinks it's necessary," said a Judiciary Committee spokeswoman.

Senate leaders Thomas A. Daschle, left, and Bill Frist support the Senate bill to crack down on illegal Internet downloads.