BILLINGS, MONT. -- Environmental groups have sued to block a federal rule that would allow state wildlife agents and private citizens to kill more endangered gray wolves in the northern Rockies.

Federal officials want to empower state wildlife agencies to kill off packs of wolves in Idaho, Wyoming and Montana if they are having a "major impact" on big-game herds, particularly elk. The rule also would allow for the killing of wolves caught attacking stock animals or dogs.

Environmental groups say that as many as 600 of the region's 1,500 wolves could be killed. Seven groups announced Monday they had filed suit in U.S. District Court in Missoula to block the rule.

Wolves rebounded from near-extinction in the region over the last decade, after they were reintroduced to Yellowstone National Park and central Idaho.

Earthjustice attorney Doug Honnold, who filed the suit on behalf of the groups, said the federal government had caved to pressure from state officials who "want to kill those wolves as soon as possible."

State and federal officials responded Monday that far fewer wolves -- possibly in the dozens -- would be killed.

The U.S. Fish and Wildlife Service is preparing to remove wolves from the endangered species list next month. All three states could then set public hunting and trapping seasons for wolves. If the number of wolves dropped below 300, they would be relisted.
© 2008 Associated Press