Washington ? A court-appointed investigator has resigned from his job probing the federal government’s management of hundreds of millions of dollars owed American Indians, and he charged that the Department of Interior blocked his work in order to conceal its deals to enrich energy companies and cheat tribes.

In his resignation letter, made public Tuesday, Special Master Alan Balaran said the Bush administration worked to thwart him beginning last summer after he uncovered a two-decades-old practice by Interior officials of negotiating leases with oil and gas companies that gave American-Indian landowners a small fraction of the royalties that private landowners received in similar deals.

Balaran accused the Department of Justice and the Interior department of trying to have him removed from the case “to prevent any further investigation” of the lopsided deals.

“A full investigation into these matters might well result in energy companies being forced to repay significant sums to individual Indians,” Balaran wrote to the judge overseeing a multibillion-dollar lawsuit by American Indians against the Interior Department.

“Interior could not let this happen … Billions of dollars are at stake.”

Interior officials released a statement Tuesday calling Balaran’s charges “preposterous” and “based entirely on innuendo, supposition and baseless speculation — just the sorts of things to which a competent judicial officer would give no credence.”