A federal judge lacks the authority to oversee reforms in a $500 million system of trust funds for American Indians, Justice Department lawyers argue in a challenge of the judge's ruling.

U.S. District Judge Royce C. Lamberth ruled last month that the federal government violated its responsibility to safeguard the money in more than 300,000 accounts for individual Indians. Lamberth put himself in charge of supervising efforts to fix problems with the accounts, requiring the government to file progress reports.

The Justice Department asked a federal appeals court Monday to consider a challenge to the ruling. The court could reject the request or decide to hear arguments on the appeal from both sides.

Government lawyers argue that the Interior Department should be allowed to finish reforms directed by a 1994 law before any court intervention, and that the judge should be able to intervene only after the department's plans are completed or if they are delayed improperly.

An attorney for the Indians said yesterday that he was puzzled by the challenge. Interior officials had said they were pleased that Lamberth did not put the trust system into receivership, Native American Rights Fund lawyer Keith Harper said. "We rarely see people appeal what they define themselves as victories," he said.

A group of Indians sued the Interior and Treasury departments in 1996 over more than a century of mismanagement of the trust funds. The accounts include proceeds from leases of Indian lands for grazing, oil drilling and the like.