After years of struggles to confine the country's largest public herd of wild bison within Yellowstone National Park, officials in Montana are weighing plans to allow the hulking beasts to roam farther into their state. Montana officials on Tuesday are set to consider plans to drastically increase the amount of land outside the park where bison would be permitted, the latest in a long history of sometimes contentious measures to control Yellowstone's growing bison population. Environmentalists, hunters and Native American groups support the proposal, which would return the bison herd, 4,600 strong before the winter, to more of its original habitat. But ranchers and some residents of nearby communities are fighting it, saying free-ranging bison would expose their cattle to disease and trample their land. Hunting is forbidden within Yellowstone, which straddles Wyoming and Montana, and most bison are allowed to leave only during certain times of year. The proposal would allow them to roam year-round, giving hunters wider opportunities to kill them and reduce the herd to a more manageable size. "We're way overpopulated," said Christian Mackay, of Montana's Department of Livestock, one of the agencies behind the proposed habitat expansion. It costs about $500,000 a year, or 5% of his department's budget, to haze wayward bison back into the park and otherwise manage them, he said. Yellowstone officials favor the expansion, saying it would help long-term conservation. "The more areas we have where bison can be managed as wildlife among society, the more opportunity we have for the public to understand that you can live with bison," said Dave Hallac, the park's head of resources. Montana's limited hunting season triggered controversy earlier this month when a member of the Blackfeet tribe, upset about the hunting of pregnant bison in winter by the Nez Perce tribe, unsuccessfully tried to deliver a bloody bison heart to Montana Gov. Steve Bullock, a Democrat. The protester was trying to raise awareness of what he called disrespectful hunting practices. Tribal representatives didn't respond to requests for comment. After nearly disappearing by 1900, Yellowstone bison, which some call buffalo, have bounced back so strongly that they are straying and causing problems in nearbycommunities, some of which have responded with lawsuits. A group of state and federal agencies has been overseeing the bison herd with the goal of keeping its numbers around 3,000 as a result of some of the legal disputes. But doing so has proved difficult. Officials have tried a variety of strategies, ranging from killing animals that wander too far out of Yellowstone to issuing limited numbers of bison-hunting licenses. Periodically, managers also ship wild bison to the slaughterhouse. The expansion would increase the habitat where bison are tolerated outside the park to about 420,000 acres year-round from roughly 40,000 acres mostly used seasonally. Its aim is to reduce tensions by allowing fairer, free-range hunting, proponents said. The plan also would allow tribal hunters to kill bison in the fall, their traditional hunting time, when cows aren't pregnant, said James Holt, a member of the Nez Perce tribe, one of four with hunting rights in the area. "We do our best to honor the buffalo when we take their lives to feed our families, but we know the timing of this is all wrong," Mr. Holt said of the current arrangement. Bison also would be less likely to encounter livestock if they are spread out in a bigger territory, supporters add, and thus less likely to infect them with brucellosis, a bacterial disease that can cause abortions and which ranchers fear could spread to their cattle. Half the Yellowstone herd has been exposed to brucellosis, though Montana officials said there are no documented cases of bison, rather than elk, passing the disease to cattle. The bulk of the new habitat would be in federal and state land, where state officials say there are few cattle. Still, ranchers say, the risk of contamination exists, and they bear the burden of vaccinating their animals. Montana requires cattle in a four-county zone around Yellowstone to be tested before they are shipped outside the area, a burdensome and time-consuming task, ranchers said. Bob Sitz, a fourth-generation Angus cattle breeder, said it should be up to Yellowstone managers, not the state, to keep bison populations at target levels. "Those bison don't do anything else for us in Montana except costing us more money," he said. Some Montana hunters openly welcome the prospect of expanded bison hunting. The state's Fish, Wildlife and Parks Department receives some 10,000 applications for the 50 or so licenses it grants each year, agency officials said. "They are a tremendously large, strong animal and a challenge as a hunter to make a good clean kill," said Chris Marchion, a retired computer-security analyst in Anaconda, Mont., who supports hunting as a conservation measure. "When you do, you really have a tremendous amount of great quality meat."