Bob Miller, a fourth-generation farmer in Oregon's Cascade-Siskiyou National Monument, is ready to call it quits.

He grazes 150 head of cattle on mountainous federal land that provides crucial forage for his herd, but he is well aware that in a matter of years, the government may push him off after completing a multimillion-dollar study on how ranching is affecting the local ecology.

"This study has become a big albatross," Miller said. "They're going to have to buy us out one way or another. We think they better do it now."

Miller and about a dozen other ranchers in Cascade-Siskiyou own federal grazing permits, lifetime permits that allow them to graze cattle for less than $1.50 a month apiece on the public land. But with concern intensifying about what grazing is doing to the land and the rare species that depend on it, he and others are making common cause with environmentalists who want to end the practice.

These overtures have encouraged environmentalists such as Rod Mondt, Southwest representative for the National Public Lands Grazing Campaign, a coalition to stop livestock grazing on public lands.

"All of a sudden we're starting to sit down with the ranching community," Mondt said. "The collaboration is starting to build."

But the nascent push to end federal grazing in Oregon, Arizona and elsewhere has sparked a backlash from several cattlemen's associations, as well as some Republicans in Congress. The debate over how to treat the ranchers underscores the growing political and economic tension over the federal government's decades-old policy of promoting grazing on federal land with low-cost permits.

No one argues that the policy is a moneymaker. Last year the Bureau of Land Management took in nearly $12 million in grazing receipts, officials said, but it spent $50 million administering the program. Critics say the true cost is at least twice as high, noting that the figures do not include expenses such as range development and predator control.

"All of our programs are money-losing," said Jim Hughes, deputy director for policy and programs at the Bureau of Land Management. "Congress said it was in the public interest to maintain a viable public grazing industry in the West."

But activists on both sides of the debate differ on whether ranching is a boon or a threat to sensitive federal lands. Mike Byrne, a rancher in Tulelake, Calif., near the Oregon border, said he and other ranchers help preserve range land by keeping vegetation in check.

"The environment as a whole is in better shape when we're there than when we're not," said Byrne, who compared ungrazed land to a haunted house. "It's a lot better to have somebody take care of the land than to allow it to go decadent."

George Wuerthner, ecological projects director for the California-based Foundation for Deep Ecology, disagrees. He said grazing and other livestock activities compact the soil, which can lead to flooding, spread invasive species and drain moist woodlands that other plants and animals depend on for sustenance. According to Agriculture Department statistics, he noted, grazing has been linked to the perilous state of 22 percent of threatened and endangered species.

"Livestock production is the single biggest negative economic impact across the western United States," Wuerthner said.

Environmentalists have been pushing to end federal grazing for years. They question why the federal government would permit grazing for minimal fees, when they could leave the land ungrazed.

But some ranchers say the alternative could be worse -- if ranchers lose their permits, they might sell their own adjacent land to developers.

Environmentalists, said Chandler Keys, vice president for government affairs for the National Cattlemen's Beef Association, are telling ranchers "to get in your pickup and get the hell out of Flagstaff. That rancher is an integral part of the system, whether you like it or not."

But after decades of feuding with environmentalists, some ranchers have changed sides. Some feel pressured by federal regulation; in other instances, they simply cannot earn the living they used to.

John Whitney III started ranching when he was 14, and he still owns the Circle Bar Ranch, an hour's drive northeast of Phoenix. But he no longer owns the 1,250 cows he once did: The U.S. Forest Service forced him to take them off its land in 2000 because of a drought that has devastated the landscape, and he lost his appeal two years later.

"We're pretty much done on federal land," Whitney said. "It's not a good business environment anymore."

Whitney is one of about 160 Arizona ranchers who back buyout legislation that would pay them $175 for each "animal month unit," the amount of forage needed to sustain a cow and calf for one month. Under current rules, the federal government determines each year how long ranchers can graze their herds by allocating them a set number of animal month units.

A bipartisan group of lawmakers has filed two ranching buyout bills, one that would reach nationwide and cost $100 million, and a smaller one aimed just at Arizona ranchers. A buyout would be "a sensible policy," said Rep. Raul M. Grijalva (D-Ariz.), one of the plan's authors, who spent his first five years living on a ranch where his father worked as a cowboy. "It's a voluntary act. It doesn't push anybody out."

But Brian Kennedy, a spokesman for House Resources Committee Chairman Richard W. Pombo (R-Calif.), called the proposal "dead on arrival," saying the bill would essentially "end grazing and ranching in the West as we know it." Hughes at the Bureau of Land Management said the administration also opposes the buyout, questioning where the government would find the funds to pay for it.

But environmentalists say the buyout will save money in the long run, and Whitney said he and other ranchers believe a buyout would have a "50-50 chance" of success in Arizona.

"Economics will dictate it," he predicted. "A lot of people don't like cows anymore, they don't want them out on federal land."

Bob Miller, a fourth-generation farmer, is ready to quit grazing cattle in Oregon's Cascade-Siskiyou National Monument.