n the annals of the digital copyright wars, major media companies facing the threat of Internet piracy have so far triumphed decisively over their challengers, who argue that the public's interest is being sacrificed to provide copyright holders with greater control.
But legal experts said the Supreme Court's decision yesterday to hear a case challenging the constitutionality of a 1998 law that extended the term of copyrights by 20 years may serve to realign the balance in favor of those who want more works in the public domain.
Even if the court ultimately upholds the law, the case is likely to focus public attention on a debate that has broad implications for the way creative work is produced and consumed, but that has so far been largely limited to lawyers and business executives.
"Merely the fact that the court will hear and decide on this case is of huge importance," said James Boyle, an intellectual-property professor at the Duke University School of Law. "It will crystallize the concerns over the state of the public domain."
At first glance, the case, Eldred v. Ashcroft, appears to have little to do with the perils and promises of distributing copyrighted works over the Internet. At issue is whether Congress overstepped its authority to grant copyrights "for limited times" to "promote the progress of science and useful arts."
In 1790, the maximum copyright term was 28 years. Now it can last more than 100 years.
But Lawrence Lessig, a Stanford Law School professor who represents the plaintiffs, said the issue had greater significance today because of the Internet. The medium would make possible a broad range of creative expression, he said, if people did not have to track down and pay for the rights to material that could be freely available to the public.
"Before the Internet, a creator's ability to put new works out there all depended on commercial publications, because only they could afford the cost," Mr. Lessig said. "But at this stage, it becomes important to establish the principle that the public domain is here and meant to be perpetually fed by works passing into it after a limited copyright protection."
It is hard to gauge the economic impact that overturning the law would have on copyright holders. The Walt Disney Company is often singled out as an example of a business that profited from public domain — drawing on works like Victor Hugo's "Hunchback of Notre Dame" and Hans Christian Andersen's "Little Mermaid" to make movies that enriched both the modern culture and its shareholders — and now profits from closing it off.
But a spokesman for Disney said that it supported the law primarily because it brought the United States into conformity with European copyright law. "The things we used from the public domain are centuries old," said John Dryer, a spokesman for Disney. "If this law is upheld, which we fully expect it will be, it doesn't place a burden on anyone."
In any case, Disney is pressing its case on other copyright fronts at the moment.
The term-extension battle is being waged amid a larger fight that pits copyright holders against the spread of technology that allows almost anyone to easily copy and distribute almost any work online.
Disney's chairman, Michael D. Eisner, is expected to testify before the Senate Commerce Committee next week in favor of a draft bill that would mandate that anti-copying technology be built into computers and consumer electronics to safeguard digital television broadcasts.
Disney is also one of several other major media firms that has filed copyright-infringement suits against several successors to Napster, the Internet music-swapping service that has been hobbled by court order.
The major movie studios are also seeking an injunction against SonicBlue, the maker of the Replay digital video recorder, because its most recent model allows consumers to send TV programs they have recorded over the Internet.
And the studios are continuing to prosecute a case against a magazine that published a computer program that could be used to circumvent the copy controls on DVD's.
A federal appeals court panel found the magazine violated the terms of another 1998 copyright law, the Digital Millennium Copyright Act, by publishing and linking to the program.
The magazine, 2600, has appealed the case to the full Court of Appeals for the Second Circuit.
It is in the broader context of these copyright battles that some legal experts and public advocates are greeting the Supreme Court's decision to hear the Eldred case as a potential shift in the judiciary's treatment of copyrights.
"If those who defend the public interest in copyright can win this battle," said Siva Vaidhyanathan, an assistant professor of information studies at the University of Wisconsin, "that means the Supreme Court will have once again clearly defined that copyright is supposed to work for the public and not a small set of corporations."