Federal protection for gray wolves in the Northern Rockies ends today.

But environmental groups say they are moving forward with plans to sue the U.S. Department of the Interior to keep wolves on the endangered species list.

A coalition of 11 environmental groups notified the federal government when the delisting was announced that they would file suit in 60 days, the first step for litigation under the Endangered Species Act. The federal government announced the delisting decision last month.

The coalition's attorney, Doug Honnold of Earthjustice, said he would file suit in federal court April 28. The coalition hasn't decided where to file, but Missoula is an option, he said.

Honnold said he would seek an immediate court injunction if state game officials start to kill wolves before the lawsuit is filed.

Montana, Idaho and Wyoming, which have taken over wolf management from the U.S. Fish and Wildlife Service, plan to start wolf-hunting seasons in the fall.

Montana has regulated wolves as a big-game species, but some wolves in Wyoming and Idaho are classified as predatory and can be killed year-round.

"We don't plan to seek an emergency injunction at this point, but we're watching what the states are doing over this next 30 days," Honnold said. "If the states get out of hand, we'll figure out a way to get into federal court to stop the killing."

An estimated 1,500 gray wolves live in the Northern Rockies, where they were nearly exterminated by the 1930s. Wolves were given federal protection in 1974.

Canadian wolves recolonized Montana in the early 1980s, while wolves were reintroduced in Wyoming and Idaho in the mid-1990s.

Federal rules require Montana, Idaho and Wyoming to maintain a minimum of 300 wolves.

But agency officials say they are committed to maintaining at least 450 and that the actual population likely will be about 1,000.

Environmental groups say at least 2,000 wolves are needed to maintain a healthy population and that wolf numbers will be decimated by legalized hunting and loosened restrictions on when wolves can be killed to protect game herds.

The region's wolf population is increasing by about 24 percent annually, according to wildlife officials.