Just pick a number, lawmakers were told Wednesday by both sides looking to Congress to resolve a lawsuit over billions of dollars in federal royalties that American Indians claim they are owed.

Estimates of the money owed for unpaid royalties on oil, gas, timber and other resources from Indian lands range from half a billion dollars to $27.5 billion, a panel of negotiators and tribal leaders told Senate and House members.

Many people with a stake in the bitter class-action lawsuit against the Interior Department are now convinced that only Congress can settle it equitably. And many now believe an arbitrary decision could be fairer than any technical, data-driven fix.

"One number's as good as another?" asked Sen. John McCain, R-Ariz., the chairman of the Senate Committee on Indian Affairs.

"Ultimately, this is an arbitrary solution. There is no right number," mediator John Bickerman told a joint hearing by McCain's committee and the House Resources Committee.

No one disputes that the government has done a poor job handling the Indian trust funds in the past, he said. The only question, he added, is how to put a value on that liability.

The tribes' $27.5 billion estimate is based on the presumption that Indians are still owed about a fifth of the $100 billion to $170 billion in royalties they should have received, most of that accrued interest. The government's much lower figure is based on efforts to account for possible errors in collections, deposits and payments.

Congress created the federal trust to handle Indian royalties in 1887. It demanded an accounting in 1994, and two years later Elouise Cobell of the Blackfeet Indian tribe and others filed suit when the accounting was still not done.

"This trust system was imposed on people, we didn't ask for it," said Mike Marchand, the first vice president of Affiliated Tribes of Northwest Indians. "We're doing the best we can to work with the system."

Marchand looked to Congress, saying a court settlement "seems to be getting farther and farther away every day." He complained that Bush administration officials "don't seem to have a lot of knowledge about life on our reservations or how to communicate."

Since the case was filed, U.S. District Judge Royce Lamberth in Washington has been sharply critical of the government's problems showing how it handled the royalty money held in trust for Indians.

Lamberth has twice ordered the Interior Department to disconnect its computers from the Internet for failing to provide adequate security for the Indians' trust records. He has held Interior Secretary Gale Norton and her Clinton-era predecessor, Bruce Babbitt, in contempt.

Rep. Richard Pombo, R-Calif., the House committee's chairman, said it would take a miracle for either side in the dispute to propose "an acceptable amount" for a legislative settlement. There are several bills pending in Congress, but they leave blank the settlement amount.

"If we don't do this, the case will drag through the courts as it has dragged on for the last 10 years," Pombo said. "And all Indian Country suffers, because rightly or wrongly, scarce federal resources meant for important tribal services are being diverted to deal with it."

An independent administrative tribunal to process claims — similar to what was done to help make reparations after World War II — could be established, said Stuart Eizenstat, a former undersecretary of state in the Clinton administration. Eizenstat negotiated the historic agreement with Switzerland's two largest banks to pay Holocaust survivors $1.25 billion.

"You cannot have courts settle historical wrongs," he said. "They cannot settle a case like this, where the evidence is poor, the number of claims is uncertain."

Eizenstat, too, acknowledged "an element of arbitrariness" in any solution.

"There'll never be litigation that satisfies both sides," he said. "How do you measure the injustice to American Indians who misplaced their trust in the government?"