A federal judge ruled Tuesday that the Bush administration violated the Endangered Species Act when it relaxed protections on many of the nation's gray wolves.

The decision by U.S. District Judge Robert E. Jones in Portland rescinds a rule change that allowed ranchers to shoot wolves on sight if they were attacking livestock, said Michael Robinson of the Center for Biological Diversity, an environmental group.

In April 2003, the U.S. Fish and Wildlife Service divided the wolves' range into three areas and reclassified the Eastern and Western populations as threatened instead of endangered. The Eastern segment covers the area from the Dakotas east to Maine, while the Western segment extends west from the Dakotas. The agency left wolves in the Southwest classified as endangered.

But the judge ruled that the government acted improperly by combining areas where wolves were doing well, such as Montana, with places where their numbers had not recovered.

"Interior Secretary Gale Norton tried to gerrymander the entire contiguous 48 states so that wolves in a few areas would make up for the absence of wolves in much larger regions," Robinson said. "Now, instead of drawing lines on the map based on political considerations, any future lines must be based on science."

The judge also found that Fish and Wildlife did not consider certain factors listed in the Endangered Species Act in evaluating the wolf's status, including threats from disease, predators or other natural or manmade dangers.

Fish and Wildlife expressed disappointment in the ruling.

"We believe our rule provided for biologically sound management of the core population of wolves in areas where we knew they could thrive as stable viable populations," the agency said in a statement. "We also believe the rule was correct as a matter of law under the Endangered Species Act."

Mike Senatore, vice president of Defenders of Wildlife, said the ruling would make it more difficult for the Bush administration to reduce or eliminate Endangered Species Act protection for other species.

Practically speaking, only wolves in northwestern Montana were affected by the rule change that allowed ranchers to shoot wolves on sight, said Ed Bangs, wolf recovery coordinator for the Fish and Wildlife Service. The rule never extended to experimental populations in Yellowstone National Park, Wyoming, Idaho and the rest of Montana, and no packs have been established in other states in the region, Bangs said.

"We haven't had a wolf killed by a private citizen defending private property since the new rule went into effect," Bangs said.

By the 1970s, wolves had been virtually wiped out in the Lower 48 states to protect livestock.

Gray wolves were reintroduced in and around Yellowstone in 1995 and 1996, and federal wildlife officials have declared their recovery a success. Officials estimate there are now more than 800 wolves in Montana, Idaho and Wyoming, including Yellowstone National Park.

In the Eastern sector, there are an estimated 3,200 wolves in Minnesota, Wisconsin and Michigan.

A small number of Mexican gray wolves were reintroduced in the Southwest in 1998.