Entire packs of endangered gray wolves may be killed under new directives from Montana Gov. Brian Schweitzer.

Schweitzer ordered wildlife officers not to investigate or prosecute ranchers who shoot wolves that attack livestock, and he authorized the killing of entire packs that endanger livestock or elk.

The Democratic governor outlined his initiative Wednesday in a defiant letter to Interior Secretary Ken Salazar, a copy of which was published on Schweitzer's website.

"At this point, I can do nothing less and still maintain my commitment as Governor to uphold the rights of our citizens to protect their property and to continue to enjoy Montana's cherished wildlife heritage and traditions," Schweitzer wrote.

Montana livestock producers are frustrated over rules that protect wolves, which were hunted to near-extinction in the early 20th century.

Gray wolves killed livestock at a rate of one animal per day in 2009, including 148 sheep in one herd in August that year, the Missoulian newspaper reported.

Kendra Barkoff, a spokeswoman for the Department of Interior, told the Missoulian that wolf management should be turned over to states with approved management plans.

"But the governor's letter is not the answer," she added.

"It's unnecessarily heavy-handed," said Mike Leahy, director of the Rocky Mountain region for Defenders of Wildlife. "Any concerns that wolves create can be addressed in a targeted fashion, and there's no reason for states to start whacking wolves in large numbers."

"The frustration over wolf impacts on the ground is overblown," he added. "These are impacts that are manageable."

Gray wolves were listed as an endangered species in 1973. They were briefly delisted in 2009, but a 2010 federal court order put them back on the list (PDF), and the federal government issued a rule in October to comply with the order.

Montana's two U.S. senators, Democrats Max Baucus and Jon Tester, introduced legislation last week to remove gray wolves from the endangered species list.

As of December 2009, there were 319 wolves in the Northwest Montana population zone (PDF), 173 of them adults, according to the U.S. Fish and Wildlife Service.

There were 106 in the Yellowstone National Park population zone (PDF), where wolves were reintroduced as an experiment in the mid-1990s.