PINEDALE - A conservation group asked a federal judge Wednesday to halt further drilling within the booming Pinedale Anticline natural gas field in western Wyoming.

The Theodore Roosevelt Conservation Partnership claims the government has reneged on promises to shield deer, sage grouse and other wildlife from energy development in the area. The geologic formation in Sublette County has an estimated 21 trillion cubic feet of natural gas - one of the largest reserves in the United States.

About 1,000 wells have gone in so far, and a pending plan would allow 4,400 more over the next 60 years.

The fast pace of development, coupled with the presence of large numbers of deer, grouse, antelope and other game species, has made the area a signature battleground for the Bush administration's pro-energy policies.

Federal and industry officials say rapid development of oil and gas fields across the West is critical to meet rising energy demands. Environmentalists say the drilling is moving too fast, leaving environmental devastation in its wake.

Wednesday's lawsuit filed in U.S. District Court in Washington, D.C., accused the Bureau of Land Management of authorizing drilling on the Anticline despite the agency's own predictions that wildlife populations will decline. It also said the agency had failed to follow through on a 2000 commitment to monitor wildlife and restore declining populations.

"This is an area with world-class wildlife populations," said Katie McKalip with the Theodore Roosevelt Conservation Partnership. "The BLM violations have resulted in severe damage to wildlife across the Anticline."

The group's attorney, Tom Wilmoth, said the lawsuit does not seek to stop gas production from existing wells. Rather, it would force the government to address wildlife issues before more drilling was permitted.

A BLM official said the agency was aware of some wildlife declines, including a 46 percent drop in mule deer numbers on the Anticline that was documented in a recent industry-sponsored study.

But Bill Lanning, associate field manager for the BLM's Pinedale office, said the agency has worked with companies to reduce those impacts since they became apparent.

Most development is now done through directional drilling, meaning multiple wells drilled from a single site. Also, pipelines have been installed to reduce truck traffic that can kill wildlife or scare it away.

"We are enabling the companies to enjoy the rights of (developing) their leases but cutting back the area they can use to accomplish that," Lanning said.

The litigation comes as three companies - Shell Exploration and Production, Ultra Resources and Questar Exploration and Production - have asked for the removal of some drilling restrictions to speed up new well installations.

Current rules shut down development for months at a time during wildlife breeding and migration seasons.

Company representatives contend that by working year-round on some areas of the Anticline, they could drill, remove most equipment and then restore the landscape more quickly.

"We believe we can develop the field better," said Deena McMullen with Shell. "We know more about the resource and how we can efficiently develop that resource and further reduce the effects to wildlife and habitat."

McMullen said her company believes the BLM has met its environmental obligations under the 2000 plan that opened up drilling on the Anticline.

That's not the view of Linda Baker, former chairwoman of a BLM-appointed advisory group for the Anticline. Baker, coordinator for the Upper Green River Valley Coalition, said the agency had ignored early indications of wildlife troubles - and must now face up to that in court.

"We've been saying this for years. They didn't like what we were saying when we were saying, 'Slow down,'" she said.

The lawsuit was assigned to District Judge Richard Leon.