Griles, the department's deputy secretary, said he plans to leave office by the end of January and return to private business.

In a career shuttling between regulating private energy interests and lobbying for them, he secured a reputation as a go-to broker in Bush's program to lease out vast oil, gas and coal reserves below federally owned land in the West.

''I have been a regulator almost all my life. And, yes, I was on the private sector side, and it did have oil and gas in it. But that taught me about what the government does right, and what the government does wrong,'' he told The Associated Press on Tuesday.

Griles says his 22 years in public service, half at Interior and half overseeing Virginia's parks, forests and mining, helped improve national parks, forests and rivers.

''I hope I can continue working on the outside to accomplish what I helped address on the inside over the past four years - balancing our national economic prosperity with our ongoing determination to clean up our environment,'' he said.

During nearly half his tenure at Interior since July 2001 he was being investigated by the department's inspector general. Inspector General Earl Devaney concluded Griles didn't appear to violate ethics rules arranging meetings between Interior officials and former clients and partners, or in the award of $1.6 million in contracts to a former client.

But Devaney described Griles' behavior as an example of ''an institutional failure'' among Interior officials who potentially eroded public trust by failing to consider the perceived impropriety of their actions.

Griles continued to receive $284,000 a year, in addition to his Interior salary, as part of a four-year severance package from his former lobbying and consulting firm.

''I have had some very difficult issues to make in my career,'' he said. ''I've always been fair and balanced. I have never denied any environmental or conservation groups or activists access to my office.''

The Wilderness Society calculates that Interior, under Secretary Gale Norton and Griles, has opened at least 160,000 public acres of potential wilderness, mainly in Utah and Colorado, to oil and gas drilling.

Interior officials call that figure a distortion.