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Justice Stevens, in his dissenting opinion, called the extension a windfall for current copyright owners. "Members of the public were entitled to rely on a promised access to copyrighted or patented works at the expiration of the terms specified when the exclusive privileges were granted," he said, while copyright holders have no reason to complain if they do not receive more protection than they were originally promised.

Justice Stevens said the decision left Congressional action in the copyright area "for all intents and purposes judicially unreviewable," adding, "That result cannot be squared with the basic tenets of our constitutional structure."

In quoting Chief Justice John Marshall's famous words from the Marbury v. Madison decision in 1803 — "it is emphatically the province and duty of the judicial department to say what the law is" — Justice Stevens may have been tweaking the majority in the series of federalism cases in which he has been a consistent dissenter as the court has invalidated numerous acts of Congress. Chief Justice William H. Rehnquist and his allies in those decisions have frequently quoted the line from the Marbury decision as justification for the court's active role in policing the federal-state boundary.

Professor Lessig himself cited the federalism cases last year as part of his effort to persuade the court to hear his appeal, Eldred v. Ashcroft, No. 01-618, after two lower federal courts here had earlier rejected his attack on the 1998 law. The court should take the same skeptical stance toward Congress's exercise of its copyright authority as it has toward other congressional actions, he argued then.

Expressing his disappointment today, Professor Lessig said, "The impossible thing is, How do people on that court believe Congress's power is so constrained sign onto an opinion that says Congress's power is not constrained?"

Jack Valenti, president of the Motion Picture Association of America, said the ruling was "a victory for consumers everywhere" because "copyright, whose aim it is to provide incentive for the creation and preservation of creative works, is in the public interest."

In her majority opinion, Justice Ginsburg insisted that the proper stance for the court toward Congress in this context was a deferential one. The law, formally known as the Copyright Term Extension Act, "reflects judgments of a kind Congress typically makes, judgments we cannot dismiss as outside the legislature's domain," she said.

The court noted that the extended term made the United States consistent with the copyright policy of the European Union.

The plaintiffs had also challenged the law under the First Amendment as a suppression of free expression, but the majority rejected that argument as well. Copyright law "contains built-in First Amendment accommodations," Justice Ginsburg said, including the concept of "fair use" that permits copyrighted material to be reproduced for scholarship and other purposes.

In a web-exclusive column, Linda Greenhouse answers readers' questions on Supreme Court rules and procedure. E-mail Ms. Greenhouse a question at scotuswb@nytimes.com.Please include your name, address and daytime telephone number; upon request names may be withheld.