A Viacom spokesman said the company had repeatedly asked YouTube to filter out its programming automatically, but that Google had not responded.

"They choose not to filter out copyrighted content, " said the spokesman, Carl D. Folta. He added that the company apparently had the technology to filter out pornography and hateful material, which is rarely seen on YouTube.

Chad Hurley, the co-founder and chief executive of YouTube, said the company was still working on its filtering technology. He said it had agreed to use it to identify and possibly remove copyrighted material from Warner Music, and it would discuss a similar arrangement with Viacom as part of a broader deal.

Mr. Folta said he found that stand unacceptable. "They are saying we will only protect your content if you do a deal with us — if not, we will steal it."

Whether YouTube is stealing content by serving up clips of copyrighted programs is very much up for debate. Like most big Internet companies, Google claims it is protected by the Digital Millennium Copyright Act, so long as it removes material whenever a copyright owner requests it.

John G. Palfrey Jr. , the executive director of the Berkman Center for Internet and Society at Harvard Law School, said Google may well be able to use this defense, but "I don't think the law is entirely clear." And if Google loses, "the damages could get astronomically high," he said.

Viacom's move comes at a time when it and other media companies have contemplated creating a service to rival YouTube. There have been on-again, off-again negotiations among a variety of companies, including the News Corporation, NBC Universal and the Walt Disney Company.