DENVER  The Bush administration on Thursday announced an end to federal protection for gray wolves in Montana, Wyoming and Idaho, concluding that the wolves were reproductively robust enough to survive.

“Wolves are back,” said Lynn Scarlett, the deputy secretary of the Department of the Interior, in a telephone conference call with reporters. “Gray wolves in the northern Rocky Mountains are thriving and no longer need protection.”

A coalition of wildlife and environmental groups dismissed the government’s claims and announced plans for a lawsuit to reverse the decision, which is to take effect next month.

Advocates for the animals said there were too few wolves to make a genetically sound population, and that state plans to manage wolf populations were underfinanced and fueled by a long-simmering animosity against wolves that could drive them back to threatened status.