When hunters legally killed 569 potentially diseased bison outside Yellowstone National Park two winters ago, critics complained that they wounded Montana's proud reputation as a refuge for wildlife.

Now officials are thinking of modifying the hunt to make it clear that the purpose is to keep Montana cattle herds disease-free. But conservation and animal-rights groups still aren't satisfied.Montana's Department of Fish, Wildlife and Parks is considering a change in rules that now call for state game wardens and national park rangers to join private hunters in killing adult bison that cross from Yellowstone into Montana in search of winter forage.

"I think the plan we have now is a good plan and will work," Gov. Stan Stephens said in a recent interview.

But the New York-based Fund for Animals has sued to stop all bison killing. The Greater Yellowstone Coalition, an environmental group, says the state should consider non-lethal alternatives.

The Montana Board of Livestock, frustrated with the long debate, has asked the U.S. Department of Agriculture to quarantine Yellowstone.

About half of the 2,500 to 3,000 bison in the 2 million-acre park are believed to carry brucellosis, a disease that causes cattle to abort. Montana spent millions of dollars over a decade to eradicate brucellosis in its cattle.

"Why should we have one vestige of infection left?" asked James Glossen of USDA's Animal and Plant Health Inspection Service. "From an agricultural perspective, we don't want that reservoir of infection in Yellowstone."

Under the current plan, negotiated with the National Park Service, private hunters are called to kill bull bison, and game wardens and park rangers may be called in to kill cows that wander out of the park, sometimes onto private land. Calves would be captured, neutered and sold.

Bison that remain inside Yellowstone may not be harmed.

Officials say the plan seeks to spread the responsibility for the killings and mitigate some of the outrage that followed the killing of 569 bison by private hunters during the winter of 1988-89. Eleven have been killed so far this season.

Officials also say cows are more likely to carry brucellosis than bulls, and putting the responsibility for their killing in the hands of wardens and rangers should reduce the chances of their spreading disease.

But the Montana Wildlife Federation, a conservation group whose ranks include hunters, says the bison killing "is damaging the Montana record as a progressive wildlife conservation state."

"The eyes of all America are watching," Wayne Pacelle, Fund for Animals' executive director, said last week. "The Park Service clearly is not going to benefit by having the public see its rangers shoot its very symbol."

K.L. Cool, the state's Fish, Wildlife and Parks director, has agreed there is no sport involved in shooting the slow-moving animals, likening it to "shooting cattle in a feed yard."

He said he would be willing to consider a better alternative but that in the end the spread of brucellosis must be controlled.

Ranchers in the area are watching the debate especially closely.

"Bison in Yellowstone Park are of great value to all of us," said James Stermitz, a rancher near the park's northern gate. "Bison outside of Yellowstone Park can only offer problems that would not get better."