LANDER - The U.S. Forest Service could quash contested oil and gas leases in the Wyoming Range, if an updated environmental analysis differs from its 18-year-old predecessor.

But if that happened, it could lead to legal imbroglios between the Forest Service and the companies that purchased the leases from the Bureau of Land Management.

If the latest Forest Service analysis indicates that the environmental impact of drilling on the Wyoming Range would be unacceptable, the Bridger-Teton National Forest and its supervisor, Carole "Kniffy" Hamilton, could, effectively, invalidate the leases.

"Through the (updated environmental analysis), we will determine if new information exists which would change our previous consent to leasing the 44,720 acres," Hamilton said this week.

Groups that oppose new drilling projects in the Wyoming Range are counting on the passage of a U.S. Senate bill introduced five months ago by Sen. John Barrasso, R-Wyo., which would stop the sale of future oil and gas leases there, and allow for the buyout and permanent retirement of existing leases.

But the Wyoming Range Legacy Act still hasn't received a hearing in a Senate subcommittee, and advocacy groups are calling on the Bridger-Teton National Forest to exercise its power, and invalidate the contested leases, instead of waiting for something to happen with the Senate bill.

"The legislation is obviously the A-game; it's definitely the most important thing," said Tom Reed, a representative of Sportsmen for the Wyoming Range. "But running a close second is the 44,700 acres. It is the gateway to that whole mountain range from the east side, and there are a number of avenues outside the legislation for getting that piece of land conserved for hunting and fishing."

The BLM sold the contested oil and gas leases on the eastern slope of the Wyoming Range in 2005 and 2006. Those leases have been in limbo since just after the sales, when the Department of the Interior determined that the Forest Service's plan, which authorizes the leases, relies upon out-of-date scientific data.

The Bridger-Teton is still operating on its 1990 forest plan, which didn't anticipate the natural gas boom in western Wyoming, Reed said.

"The forest plan is old," he said. "When they last looked at it, we didn't have the level of development we have now. We didn't have the Jonah Field. We didn't have the Pinedale Anticline. In recent years things have changed almost on a six-month basis."

While the updated analysis could motivate the Forest Service to rescind its previous consent to lease the acreage, it might also reaffirm the original 1990 study, and legitimize the sales.

Bruce Hinchey, president of the Petroleum Association of Wyoming, said recent development of the Jonah and Pinedale Anticline gas fields should have little bearing on the Bridger-Teton's plan for the Wyoming Range.

"The forest plan was based upon not what was going on in the rest of the state, but in the Wyoming Range," Hinchey said.

New activity in different parts of the state shouldn't change the equation for Wyoming Range development, he said.

Hamilton implied Tuesday that the Bridger-Teton could effectively nullify the leases - if it doesn't do so following its new analysis - when it creates its new forest plan, which it intends to do in the coming months. And she indicated that public sentiment could play a significant role in that process.

"Much of the public feels that we need to develop the oil and gas resource on areas other than the Bridger-Teton National forest first," Hamilton said. "As the forest supervisor of the (Bridger-Teton), I am committed to following the direction set forth in our forest plan in making management decisions about the (natural resources there)."

Public participation in the forest plan revision process is critical, she said.

"If the public agrees that certain areas of the forest are not suitable for oil and gas leasing, then the revision of the forest plan is the place to make those changes," Hamilton said.

If the Forest Service retroactively retracts its consent for the contested leases because of the new environmental study, or if it changes the status of the acreage in its new forest plan, the interested parties will most likely end up in court, Hinchey said.

The leases were sold and issued, he said, with the understanding that the companies purchasing them would be able to develop them.

"If the Forest Service did (reverse its consent), then you would have what is called a taking - a taking of a right that was granted," Hinchey said.

The federal government could possibly be required to compensate some or all of the leaseholders for the undeveloped resources they purchased the rights to, he said.

Environment reporter Chris Merrill can be reached at chris.merrill@trib.com.