Washington ? A top Interior Department official said he was forced to quit Tuesday because he challenged the department’s claims that it is repairing a historically mismanaged trust fund for American Indians.

Special Trustee Thomas Slonaker, whose position was created by Congress to provide independent oversight for the overhaul of the fund and to report back to lawmakers, submitted his resignation Tuesday to Interior Secretary Gale Norton.

“I was given the choice of resigning or being fired,” Slonaker said in an interview. “Things have not been going well in terms of trust reform, but it’s not always the message they want to hear.”

Slonaker has clashed with Norton and department officials, offering testimony in court and before Congress that contradicted assertions of progress toward fixing the century-old trust fund designed to manage oil, gas, mining and timber royalties from Indian land.

A history of mismanagement has resulted in the loss of an unknown amount of money. Attorneys for Indians who sued the government said at least $10 million was owed to more than 300,000 Indian landowners.

The department has told Congress it would take $2.5 billion and 10 years to conduct a full accounting, but Slonaker said it was impossible because records were missing or had been destroyed.

During a hearing Tuesday before the Senate Indian Affairs Committee, American Indian leaders said they wouldn’t back down on demands that an independent commission supervise the Interior Department’s management of $1 billion a year in royalties from Indian land.

Tribal leaders want the commission to have the power to subpoena documents, audit the department’s accounting of the royalties and impose fines against the interior secretary to repair a history of mismanagement that has squandered an unknown amount of money.

Norton appointed Donna Erwin, the No. 3 official in Slonaker’s office, as a temporary replacement and in a statement thanked Slonaker for his service.