WASHINGTON - The Justice Department has launched an investigation into whether former Interior secretary Gale A. Norton illegally used her position to steer lucrative oil leases to Royal Dutch Shell PLC, the company she works for now, officials with both departments confirmed.

The criminal investigation is focused on a 2006 decision by the Interior Department to award three oil shale leases on federal land in Colorado to a Shell subsidiary. Oil from the leases could eventually earn the company hundreds of billions of dollars.

Investigators are looking into whether Norton, named by President George W. Bush to run the agency in 2001, violated a law that bars federal employees from discussing employment with a company if they are involved in a decision that could benefit that company. Months after granting Shell the leases, Norton left the agency. Shell later that year hired her as an in-house counsel for its unconventional fuels division, which includes oil shale.

Justice Department and Interior investigators also are trying to determine whether Norton violated a broader federal “denial of honest services’’ law. Under the statute, government officials can be prosecuted for violating the public trust for directing government business to favored firms.

Officials spoke to the AP on the condition of anonymity because they were not authorized to discuss the case.

Norton could not be reached immediately for comment.

“We are aware of an investigation; however, we are not in a position to comment,’’ said Kelly op de Weegh, a Shell spokeswoman.

The Interior Department’s Office of Inspector General began the investigation toward the end of Bush’s last term, after receiving complaints about the lease process. The IG’s office made a formal referral to the Justice Department earlier this year after concluding there was probable cause of a criminal violation.

The investigation was first reported by The Los Angeles Times.

Before becoming Bush’s first Interior secretary, Norton was Colorado’s attorney general and had worked as a private lawyer for timber, oil, and mining companies. At Interior, she supported expanded oil and gas drilling on government-owned land.

The development of oil shale largely in the West was one of the technologies that the Bush administration wanted to explore aggressively. In response to a recommendation by then-Vice President Dick Cheney’s energy task force, the Interior’s Bureau of Land Management issued six demonstration leases in Colorado and Utah.

Shell was the only company to receive more than one lease. Its US operations are based in Houston.

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