RICHMOND, Va. » Congress overstepped its authority when it enacted a law allowing the federal government to hold sex offenders in custody indefinitely beyond the end of their prison terms, a federal appeals court ruled yesterday.

The law allowing civil commitment of “;sexually dangerous”; federal inmates intrudes on police powers that the Constitution reserves for states, many of which have their own similar statutes, a three-judge panel of the 4th U.S. Circuit Court of Appeals said.

Civil commitment power “;is among the most severe wielded by any government,”; Judge Diana Gribbon Motz wrote. “;The Framers, distrustful of such authority, reposed such broad powers in the states, limiting the national government to specific and enumerated powers.”;

In upholding a decision by U.S. District Judge W. Earl Britt of Raleigh, N.C., the 4th Circuit became the first federal appeals court to rule on an issue that has divided courts nationwide. A judge in Minnesota reached the same conclusion as Britt, while courts in Hawaii, Oklahoma and Massachusetts upheld the measure.

Yesterday's ruling is binding only in the states included in the 4th Circuit: Virginia, North Carolina, South Carolina, West Virginia and Maryland.

U.S. Department of Justice spokesman Charles Miller said it was too early to comment on what the government might do next. It could appeal the ruling to the U.S. Supreme Court or seek a rehearing before the full federal appeals court.

Elizabeth Luck, a spokeswoman for the federal public defender's office in Raleigh, declined to comment. The public defender represented five inmates who challenged the law after they were kept in custody beyond the end of their sentences at the federal prison hospital in Butner, N.C.

Civil commitment was authorized by the Adam Walsh Child Protection and Safety Act, which President Bush signed in July 2006. The act, named after the slain son of “;America's Most Wanted”; television host John Walsh, also establishes a national sex offender registry, increases punishments for some federal crimes against children and strengthens child pornography protections. Those provisions are not affected by the ruling.

The appeals court found no merit in the government's argument that it had constitutional authority to enact the civil commitment law under the Commerce Clause, ruling that “;sexual dangerousness does not substantially affect interstate commerce.”;

The government also relied on a clause authorizing Congress to enact “;all laws which shall be necessary and proper”; for executing federal powers, but the court said that applies only to powers enumerated by the Constitution.

“;Our holding, however, does not require that the government's legitimate policy concerns go unaddressed,”; Motz wrote, suggesting federal authorities concerned about a soon-to-be-released inmate's sexual dangerousness can notify state officials, who can pursue civil commitment under state law.