BOISE, Idaho - The U.S. Fish and Wildlife Service ignored expert advice when it decided to deny federal protection to the sage grouse, and the agency must reconsider its decision, a federal judge ruled Tuesday.

In a decision highly critical of the agency and its decision-making process, U.S. District Judge B. Lynn Winmill said the service also failed to use the "best science" available when deciding not give the declining species protection under the federal Endangered Species Act.

Such protection could have dramatic consequences in Wyoming, where state and industry officials fear it would shut off millions of acres to livestock grazing and energy development.

John Emmerich, deputy director of the Wyoming Game and Fish Department, said Wyoming has vast areas of sage grouse habitat and the bird is widely distributed across the state.

"If a species like that gets listed, it'll have huge ramifications," he said.

Endangered species listing of the grouse could affect the use of both private and public land for agriculture, mining, oil and gas, Emmerich said. He hopes the work Wyoming and other states are doing to help the bird will lead to the conclusion that it's not endangered.

Erik Molvar, executive director of the environmental group Biodiversity Conservation Alliance in Laramie, said Wyoming does have relatively robust populations of sage grouse. But he said sagebrush habitat is quickly being eaten away by the BLM's policy of encouraging and accommodating oil and gas development.

"Hopefully, this court ruling will serve as a wake-up call that the BLM change its ways," Molvar said.

Winmill harshly criticized what he said was the "inexcusable conduct" of former Deputy Assistant Interior Secretary Julie MacDonald, who resigned in May. MacDonald intimidated Fish and Wildlife staffers, edited scientific conclusions and otherwise intervened in the listing process "to ensure that the 'best science' supported a decision not to list the species," Winmill said.

Joan Jewett, a spokeswoman for the Fish and Wildlife Service in Portland, Ore., said the agency had not yet seen the ruling and so she could not comment.

Sonya Jones, a lawyer with the Pacific Legal Foundation representing ranching, livestock and farming interests in Idaho, Wyoming, Oregon and Nevada, promised to appeal.

Jones said the Fish and Wildlife Service followed all the rules required by the Endangered Species Act in making its determination. Listing the bird could have harsh economic consequences, she said.

The states of Idaho, Wyoming and Colorado had sided with the Fish and Wildlife Service in the case, arguing in part that the states had spent a great deal of time and money creating their own conservation plans to protect grouse, and that those protection efforts were working. Those efforts justified the Fish and Wildlife Service decision, the states said.

Bill Myers, an attorney representing livestock and oil and gas interests and serving as local counsel for the states of Idaho and Wyoming, said his clients have not yet decided whether they will appeal.