BOISE — With domestic sheep due to be released on rangeland near Idaho's Hells Canyon next month, the U.S. Forest Service and environmentalists are back in federal court this week to argue over whether the grazing plan is legal.

Wednesday's hearing before U.S. District Judge B. Lynn Winmill in Boise is the latest theater in the fight over how best to protect wild bighorn sheep from deadly lung disease that scientists say is transmitted by their domestic cousins. Ranchers view grazing closures as a threat to their livelihood.

Last year, the Payette National Forest closed 54,000 acres to grazing, to separate the species.

Earlier this year, however, Regional Forester Harv Forsgren in Ogden, Utah, delayed shuttering another 7,700 acres in 2012, citing a congressional edict pushed through in December by U.S. Rep. Mike Simpson, R-Idaho, on behalf of sheep ranchers to halt closures for at least a year.

Craig Gehrke, the Wilderness Society's Idaho director, contends Forsgren ignored the Payette National Forest's own recommendations to continue closures and instead caved in to Simpson, the powerful leader of a House budget panel that oversees the Forest Service's annual spending.

"Somebody in the regional office or Washington, D.C., threw the Payette National Forest under the bus because they didn't want to anger the Appropriations subcommittee chairman," Gehrke said Monday.

Winmill is expected to rule soon on environmentalists' demands to continue closures, with sheep due to be turned out next month.

Under a 2010 Payette National Forest plan, grazing allotments were to be reduced 70 percent by 2013, or some 70,000 acres, near Hells Canyon. Once complete, it would protect some 94 percent of bighorn habitat in the forest.