The outcome will determine when hundreds of thousands of books, songs and movies will be freely available on the Internet or in digital libraries.
Groups challenging copyright law argued that justices should protect the public's right to material.
The Bush administration urged the court to reject the groups' appeal. Because copyrighted material can be used under some circumstances, "the concerns and values reflected in the First Amendment are therefore fully satisfied," Solicitor General Theodore Olson wrote the court.
Lawrence Lessig, attorney for the challengers, said the latest 20-year extension approved by Congress in 1998 is ill-timed and unconstitutional.
"Just as the time that the Internet is enabling a much broader range of individuals to draw upon and develop this creative work without restraint, extensions of copyright law are cosing off this medium to a broad swath of common culture," he wrote.
The challengers include organizations and businesses that specialize in former copyrighted material, like books, movies and songs. The U.S. Circuit Court of Appeals for the District of Columbia ruled that they "lack any cognizable First Amendment right to exploit the copyrighted works of others."
The Bush administration said Congress promotes progress by giving people rights to their material. The administration also defended lawmakers' decision to apply the 20-year extension to all current copyrighted material, not just future.
"Congress was entitled to establish a system of copyright that treats authors in a more evenhanded fashion," Olson wrote in the government filing.
The 1998 copyright changes, known as the Sonny Bono Copyright Term Extension Act, bring U.S. rules in line with those in the European Union.
Congress extended the term of copyright 11 times in the past century, said law professor Mark Lemley, representing the non-profit Internet Archive.
Lemley told the Supreme Court that copies of old books, movies and sound recordings are being lost before they can be archived. He said in 1930, 10,027 books were published but as of last year, all but 174 were out of print.
If it wasn't for the law, "digital archives could inexpensively make the other 9,853 books published in 1930 available to the reading public starting in 2005," he wrote. If the law "still stands, we must continue to wait, perhaps eternally, while works disappear and opportunities vanish."
Justices last reviewed a large copyright case in 1985, but the laws have changed since then.
The case is Eldred v. Ashcroft, 01-618.
By GINA HOLLAND
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