TORONTO -- A plan by the Canadian government to begin slaughtering the largest herd of buffalo in the world this winter, partly to assure disease-free beef exports, has led to a bitter confrontation between wildlife conservationists and cattle ranchers and an open rift among government departments.

Officials of the Agriculture and Health departments maintain that the slaughter of 3,500 bison and subsequent rebuilding of the herd are necessary to prevent diseased buffalo from infecting nearby cattle herds, while conservationists contend that it would be reminiscent of the liquidation of plains buffalo a century ago, when millions of the animals were killed by white hunters and sportsmen, some shooting from the windows of trains as they rolled across the prairies.

Environmentalists and Indian leaders in the north of Alberta province and in the Northwest Territories say that if the planned eradication of the wood bison herd in Wood Buffalo National Park goes ahead, it will lead to protests rivaling the 1970s international campaign that halted the killing of baby harp seals in Newfoundland.

Motivated, in part, by Canada's fear of losing its bovine disease-free status and millions of dollars in beef exports to the United States under the U.S.-Canada free trade agreement, the Agriculture Ministry is pushing ahead with plans to kill the entire buffalo herd once snowfall in the 17,300-square-mile park makes the animals easier targets for helicopter-borne hunting crews, using infrared heat-seeking equipment to guide them.

The department is expected to announce its final decision next month on the basis of a recommendation made in August by a federal environmental review panel that slaughter is the only way to eliminate outbreaks of tuberculosis and bovine brucellosis that it says have infected a third to half of the herd.

However, a leaked internal memorandum drafted by game wardens and other employees of Parks Canada, a division of the Ministry of Environment, contends that studies of the incidence of disease in the herd have not been done for 15 years, and that there is no visible evidence that disease is as widespread as Agriculture and Health department officials say.

"The park bison have been portrayed by the slaughter proponents as a pathetic herd of diseased and dying animals. On the contrary, visual evidence of the disease is rare. The bison are magnificent animals that continue to thrill all park visitors," the dissident parks employees said in the memorandum.

Some of the opponents claim that the government has a "hidden agenda" of shrinking the boundaries of the national park for the purpose of exploiting timber, natural gas, gypsum and other natural resources.

Moreover, the parks employees said, the buffalo herds are so widely scattered that it would be impossible to track down and kill all of the animals. Killing the buffalo, they contended, would "set a precedent which threatens the ecological integrity of all national parks."

Independent conservationists said that the slaughter could have other long-range environmental effects, such as depriving wolves of their primary food source and altering the habitat of other endangered species of animals and birds.

The park is also the nesting ground for the bulk of the world's surviving whooping crane population, an endangered species with fewer than 200 birds still living in the wild. Of these, 155 live and nest at Wood Buffalo Park in the summer, wintering off the coast of Texas.

The park was set aside in 1922 as a preserve for the recovery of the nearly extinct bison that once roamed freely across the prairies of Canada and the western United States.

Shortly after the turn of the century, Canadian government researchers purchased the remnants of an American herd -- about 700 head of plains bison -- and transported them to southern Alberta in an unsuccessful attempt to breed them with beef cattle. The result, historians say, was a strange hybrid of sickly, infertile animals that caught tuberculosis and brucellosis, a bacterial infection that causes miscarriages in animals. The project was dropped.

However, in the 1920s, about 6,000 plains buffalo were transported to Wood Buffalo National Park because of a shortage of grazing land in southern and central Alberta, and they began breeding with the wood buffalo there.

Canada's beef cattle have been free of brucellosis for years, and it is feared that herds wandering near the national park will encounter the diseased buffalo and become infected, said William Blumer, director of the Agriculture Ministry's animal health division.

"The government's position is fairly uniform -- kill the herd and reestablish a new herd. It is necessary in order to deal with the disease," Blumer said. He estimated that it would take 10 years to track down and kill all of the buffalo, during which time a herd of 80 healthy buffalo from Elk Island Park, near Edmonton, would be shipped to breeding pens in the park. In 10 years, it would grow to 2,000, he said.

Other government officials have warned that Alberta cattlemen could lose $250 million over 10 years if the disease spreads, and that Ottawa would have to spend $1 billion over the next 20 years to maintain disease inspection programs to safeguard the export of beef.

Opponents of the slaughter argue that the government is rushing into an "Armageddon option" on the basis of insufficient evidence that the diseases threaten cattle.

Citing a "massive lobby" led by Agriculture Minister Donald Mazankowski, who is from Alberta, Executive Director Paul Griss of the Canadian Nature Federation said, "We don't feel they've provided ample justification. There's no data on cattle becoming infected from bison in the wild. They haven't done any studies on the range of bison outside the park or any assessment of a slaughter's impact on the environment."

Griss called for an independent study by a group such as the World Conservation Union, which, along with UNESCO, has designated the park as a world heritage site.

Clayton Burke, of Fort Smith in Northwest Territories, who is coordinator for the 12,000 Dene and Cree Indians who live around the park, said, "We know that some of the buffalo are carrying tuberculosis and brucellosis, but the answer is not to kill them all. There is not one documented case of buffalo infecting cattle, so what is the rush to slaughter them?"

Burke, in a telephone interview, said the Indians depend on the buffalo for food, and that not one has ever contracted brucellosis, which appears in humans as a fever. He proposed that rather than kill the buffalo, the government create buffer zones and fence in cattle-grazing areas to prevent commingling with the buffalo.

Concerns that Ottawa is secretly planning to reduce the size of the park -- Canada's largest -- to sell resource rights were expressed by Burke and by James Fulton, a member of Parliament and the opposition New Democratic Party's specialist on the environment.

"There's a growing interest in its mineral potential. Those pressures are there, but how far the government will go in shrinking down the park is unclear," Fulton said in an interview. He said Alberta had already sold leases to timberland abutting the park to Japanese-owned pulping companies as part of a plan by the Alberta government to turn over 85,000 square miles of land in the province to development of natural resources.