WASHINGTON — A federal judge ruled Wednesday that the Interior Department is unable to complete an accounting of billions of dollars owed to Indian landholders across the country.

"It is now clear that completion of the required accounting is an impossible task," Judge James Robertson said in a 165-page decision in a federal lawsuit that alleges Interior officials mismanaged Indian trust funds.

Still, Robertson said the dispute is not hopeless.

"It does mean that the time has come to bring this suit to a close," he said of the 11-year-old lawsuit.

Lawyers for the American Indian landowners say the government could owe Indians more than $100 billion for payments and interest on oil, gas and other leases. Robertson said he plans to schedule a hearing in about 30 days to discuss how to come up with an appropriate remedy.

Elouise Cobell, a Blackfoot Indian from Montana who is the lead plaintiff in the class-action lawsuit, hailed the judge's ruling.

"This is a great day in Indian Country," she said in a statement. "We've argued for over 10 years that the government is unable to fulfill its duty to render an adequate historical accounting, much less redress the historical wrongs heaped upon the individual Indian trust beneficiaries."

Tina Kreisher, an Interior Department spokeswoman, said department officials were reviewing the ruling and would not comment before they could carefully examine it.

Jim Cason, associate deputy Interior secretary, has said previously that systemic problems do not persist throughout the department and that staff has worked diligently to do an accounting of the trust lands.

The government has offered to settle the suit for $7 billion — a proposal the plaintiffs rejected.

The agency manages more than $300 million a year in royalties and leases for 300,000 Indians nationally.

On the Web: www.indiantrust.com, Indian Trust (plaintiffs);

www.doi.gov, U.S. Department of Interior