BILLINGS -- An environmental group is claiming a proposal to let states kill packs of endangered wolves that prey on big game herds would result in the eradication of wolves across much of the Northern Rockies.

The Natural Resources Defense Council says ''nearly 600 wolves'' could be killed in Idaho and Wyoming through aerial operations that would be allowed under the U.S. Fish and Wildlife Service proposal.

But federal and state wildlife officials described the group's claim -- to be aired in nationwide television advertisements starting today -- as ''misleading.'' They said the number of wolves targeted would likely be in the dozens, and only in areas where the animals are a factor driving down elk populations.

''Wolves are here to stay, and it's time for people to understand that,'' said Steve Nadeau with the Idaho Department of Game and Fish. ''But we can't stand by and watch the most renowned elk population in the state of Idaho diminished because we can't hunt wolves.''

During a decade-long restoration effort that started with just 66 wolves, the region's wolf population has expanded by 20 to 30 percent a year. There are now an estimated 1,545 wolves in Idaho, Wyoming and Montana. That's more than five times the number federal biologists contend is needed to sustain the population.

Federal officials have announced plans to strip wolves of their endangered status by early next year, exposing the animal to public hunting for the first time in decades.

But legal challenges to the delisting are considered a certainty. If the delisting gets hung up in court, federal officials said they want states to have some way to keep wolves in check. That includes the proposal to allow states to kill wolves that prey on wildlife herds.

States would be required to maintain at least 200 wolves each. Montana officials have said they do not intend to take advantage of the program.

Peggy Struhsacker, a wolf specialist with the Natural Resources Defense Council, said she believes Wyoming and Idaho officials would kill as many wolves as possible.

''It's like dealing with them when wolves were being eradicated. The states have not progressed,'' she said, referring to wolf poisoning campaigns of the early 20th century.

Nadeau agency already has proposed killing 40 to 50 wolves in the Clearwater River drainage in northern Idaho. That's an area where elk numbers have declined due to wolves, mountain lions, bears and poor habitat.

In Wyoming, officials are developing similar plans to address troubled elk herds east and south of Yellowstone National Park, said John Emmerich, assistant director of the state Game and Fish Department. The plans were not final, but Emmerich said they could entail killing as few as 30 wolves.

Emmerich's agency has said it will ask the Wyoming legislature for $500,000 for wolf removal programs over the next two years.