By 420 to 4, the House yesterday approved an amendment that expressly prohibits Internet censorship by the government.

The "Internet Freedom and Family Empowerment" amendment to the House communications bill appears to conflict directly with an amendment to the Senate version of the same bill.

The Senate amendment, sponsored by Sens. J. James Exon (D-Neb.) and Dan Coats (R-Ind.), is called the "Communications Decency Act" and sets criminal sanctions for obscenity and indecency on-line, enforceable by the Federal Communications Commission. That bill has become a lightning rod for activists, with more than 100,000 signatures collected in an on-line petition drive against the measure.

The House amendment "is a major victory for cyberspace," said Jerry Berman, head of the Center for Democracy and Technology, an on-line civil liberties and policy group. "The Internet may have lost the battle on the Senate side. But what the House indicates is that the Internet and its supporters may win the war."

Both the House and Senate versions of the bill attempt to grapple with the problem of children encountering offensive material on-line. Although there is much dispute over just how prevalent and accessible such material is, the House amendment is based on the principle that technologies are already available to help parents control what children can find on the Internet; it also calls for on-line providers to police their own offerings.

The House amendment, introduced by Reps. Christopher Cox (R-Calif.) and Ron Wyden (D-Ore.), enjoyed support from groups on the political right and left, including the Progress and Freedom Foundation, the American Civil Liberties Union, the Cato Institute and People for the American Way, as well as all of the major commercial on-line services. Although President Clinton has threatened to veto the communications bill, he expressed support for the Cox-Wyden approach in a letter to lawmakers Thursday.

"Virtually everyone in the House shares the objective of protecting children from offensive material on-line," Cox said in an interview, "but relying on regulators and federal police won't work."

"If the government is going to send out an army of censors, that's going to spoil a lot of the Net's promise," Wyden said.

But a separate amendment to the House bill appears to conflict with the Cox-Wyden provision. The House passed changes to federal obscenity laws in an amendment sponsored by Rep. Henry J. Hyde (R-Ill.) that would criminalize some forms of on-line speech. "Just as the House closes the front door on content regulation, this . . . amendment attempts to sneak it in through the back door," said Mike Godwin, staff counsel for the Electronic Frontier Foundation.

Cox said the apparent conflict between the two House amendments could be resolved in conference committee, because "obviously the bill must not be at war with itself."

Sen. Patrick J. Leahy (D-Vt.), who led the unsuccessful opposition to the Exon amendment in the Senate, issued a statement calling the House amendment "a positive step." But Leahy warned that the Cox-Wyden effort "does not resolve the issue of content regulation on the Internet."

"I remained concerned that an exception in the Cox-Wyden amendment leaves room for the Communications Decency Act," Leahy said, referring to a provision of the amendment stating that it is not meant to conflict with the part of the federal law affected by the Exon amendment.

Leahy also warned that the Hyde amendment to the House bill "raises the continued specter of chilling the free speech rights of Internet users in slowing the free flow of information on this wonderful communications medium."

Wyden said that such concerns are valid. "Certainly the picture is not as clear going into conference as Mister Cox and I would like. . . . There is going to be much to debate in the conference."