A federal judge said Friday the National Park Service may be ordered to confine bison herds within Yellowstone National Park to keep them from being killed when they enter Montana.

"Realistically, we have to face this possibility," said U.S. District Judge Charles C. Lovell.He said Montana "is getting a bad name" because of its continuing policy of killing bison to stop the spread of infectious brucellosis, and added: "We have to ask if the status quo can continue."

He made the comments as he took under advisement a request by the national Fund for Animals for an injunction to stop the killing of bison, either by hunters, state wardens or park rangers.

He said he would rule this week.

Bison are now killed when they enter Montana to prevent the spread of brucellosis to Montana cattle.

Brucellosis is an infectious disease that causes cattle to abort their calves. Half of Yellowstone's estimated 3,000 bison are believed infected.

Montana officials say $30 million was spent over three decades to eradicate the disease from its herds, and a state veterinarian estimated that nationwide nearly $3 billion has been spent to eradicate brucellosis. Scientists say Yellowstone is the only major pool of brucellosis bacteria left.

But in 12 hours of testimony over two days, experts in veterinary medicine and wildlife biology and ecology differed on whether the threat of bison spreading the disease to Montana livestock is real or merely perceived.

They also disagreed on whether the state's plan to continue killing the bison would have any detrimental effect on the park's bison herds.

Experts called by the animal-protection group said the state was on shaky scientific ground by trying to justify the extermination of trespassing bison as a disease-control measure.

They testified there is no known instance of infected bison from the park spreading brucellosis to Montana cattle, and experts called by the state and federal government agreed on that point.

Lovell asked Mary Meagher, a federal biologist who has spent 31 years in wildlife research at Yellowstone, what could be the worst that might happen if park officials were ordered to keep bison from leaving the park.

She replied that as many as 1,000 bison might have to be killed to cull the herds, and the park might be closed to winter use by tourists. She said growing winter use of Yellowstone by snowmobilers has given free-roaming bison snowpacked routes out of the park.

Lovell pressed the experts on whether the park service actually could keep bison within park boundaries. They said it would be possible but difficult.

So far this winter, 11 bulls have been killed - none of them within 20 miles of domestic cattle.

Last winter, only four bison were killed, but attempts by animal-rights activists to disrupt the hunts drew widespread media attention.

In the winter of 1988-89, hunters and state wardens killed 569 bison from the park's northern herd, prompting a national outcry.

Since 1985, when hunters began shooting the bison, 700 cows, calves and bulls have been killed, most of them along the upper Yellowstone River.