Where the timber ends and granite stands against the clouds, four Sierra Nevada bighorn rams freeze for an instant -- noses facing the wind, horns curling from their heads, haunches taut. Then, silently, they vanish among the jagged crags and canyons between Yosemite and Mono Lake.

About 15 miles to the north, domestic sheep rancher Fred Fulstone, 85, gamely hauls his legs up a steep hillside of bitterbrush and sage. Then, giving his lungs a rest, the stockman watches somberly as government workers fasten tracking collars to five ewes. The devices are supposed to prevent his sheep from straying undetected and infecting bighorns with pneumonia.

Since the 19th century, the bighorns and Sierra sheepmen have been symbols of the wild and free-ranging Western frontier. But today they are at odds, their fate intertwined in a costly, highly politicized battle over grazing rights on public lands.

Fulstone's fight has become a focal point for bighorn-domestic sheep conflicts that sheep industry associations say could affect the grazing of 125,000 animals in California, Nevada, Arizona and South Dakota.

"It is being closely watched by the sheep industry and other livestock producers that rely on public land grazing," said Lesa Eidman, executive director of the California Wool Growers Association. "Those producers who lose access to public lands will have to cut back the number of sheep they graze, and that will have severe economic impacts on them, local communities and the industry."

Pressed by the livestock industry, environmentalists and politicians, federal officials in the Sierras have struggled to accommodate both wild and domestic sheep, which consume the same high-country brush and grasses during the summer.

Once abundant, the bighorns declined so precipitously that six years ago they were added to the federal endangered-species list. But as the population began to recover and bighorns wandered onto land used by domestic sheep, wildlife officials feared that bighorns would be exposed to a disease that could wipe out entire herds and undo a $5 million recovery effort.

Forest managers have closed some areas to commercial grazing and placed new restrictions on most of the remaining eastern Sierra sheepherders, whose industry has already been suffering from foreign competition and the loss of federal price supports for wool.

"We'll be the endangered species," said Fulstone, who has been fattening sheep on federal land for 70 years and wants the bighorns moved.

Fulstone, who had heart bypass surgery several years ago, continues to run his family's Nevada ranch, along with daughter Marianne F. Leinassar, and occasionally rides miles on a horse to check on his flocks. "We love this life," he said. "It's our culture, and should not be thrown away for 20 bighorn sheep. . . . This could ruin us."

Wildlife biologists estimate that about 350 bighorns are left in their historic range -- along 200 miles of the central and southern Sierras that is occupied partly by domestic sheep.

The bighorns had dwindled to 125 by 1999 before they were classified as endangered. The population was devastated in the 1800s by hunting. In recent decades, mountain lions and severe winters took the heaviest toll.

Now, the government draft plan for bighorn recovery cites pneumonia transmission from domestic sheep as a major threat, especially when wild rams roam widely in search of ewes during the fall rutting season. One radio-collared ram traveled 33 miles in a month.

"The problem is real," said Robert D. Williams, a U.S. Fish and Wildlife Service supervisor in Reno, Nev. "We could lose . . . years of recovery in one short [grazing] season."

In a series of experiments since the late 1980s, captive bighorn sheep died of pneumonia when they were penned with domestic sheep or were inoculated with bacteria from them.

To minimize the danger of disease transmission, federal officials have closed some parts of the mountain range to domestic sheep -- including some of Fulstone's grazing areas.

Fulstone averted more closures this summer; his flocks were allowed to graze across about 20 square miles of the Humboldt-Toiyabe National Forest. But his herders are required to make frequent counts of sheep, tend them with extra dogs and promptly report strays.

Meanwhile, state Department of Fish and Game biologists have been capturing wild rams and outfitting them with radio collars so they can be tracked from the air and the ground. And they are seeking federal permission to kill, if necessary, any bighorns that come in contact with domestic sheep.

That prospect has outraged conservationists, who want the grazing permits canceled. "It is so frustrating the livestock industry is able to wield such influence," said Peter Galvin, conservation director and co-founder of the Center for Biological Diversity. "Instead of a conservative solution, [government officials] implement these difficult-to-enforce, Rube Goldberg, unbelievably complex solutions to a simple problem. The domestic sheep should not be around the endangered bighorns."

Although his family owns 15,000 acres in Nevada and California, Fulstone says his grazing permits on 10 times that many acres of government land are integral to his annual yield of 1 million pounds of lamb and 100,000 pounds of wool.

On a recent morning, Fulstone stood among 1,500 sheep on a hilltop overlooking the Bridgeport Valley. "We were free people 60, 70 years ago," he said. "Today, there are so many rules and laws for everything."

He was there to witness radio collars being put on some of his sheep. Fulstone has also agreed to frequent counts of "marker" sheep -- with black coats, paint or bells -- and to an evacuation plan if a bighorn shows up.

Even if the bighorns do mingle with Fulstone's sheep, some experts question the soundness of the experiments that found that bighorns died of pneumonia after exposure to the pasturella bacteria carried by domestic sheep.

Annette Rink, director of the Nevada Department of Agriculture's animal disease lab, said the experiments exposed bighorns to far more of the bacteria than they would encounter on the open range.

Noting that bighorns themselves often harbor pasturella, Rink said it would be unfair and might be ineffective to ban domestic sheep from federal land. "Ranchers and farmers feed us, and they deserve to see the best science," she said. "My attitude is that domestic sheep are innocent until proven guilty."

Although there have been no documented die-offs of Sierra bighorns in recent decades, state wildlife officials are investigating a pneumonia outbreak among desert bighorns in the neighboring White Mountains. They want to know whether the disease originated from a stray domestic flock, sheep at a University of California research station or something else.

Still, state officials working on the Sierra bighorn recovery remain convinced that disease from domestic sheep is a serious threat to the bighorns and want to err on the side of caution. That is why they believe it might be necessary to kill bighorns to stop them from carrying disease from domestic sheep back to wild herds.

"I think it's the only option we have, given the proximity of domestic sheep to wild sheep," said state Fish and Game biologist Vern Bleich, head of the bighorn recovery program.

Biologist Tom Stephenson of the state Department of Fish and Game uses a telemetry device to locate bighorns in the Sierra Nevada near Lee Vinning, Calif. Some bighorn sheep have been fitted with transmitters. Biologists believe only 350 are left in their historic range in the central and southern Sierras. Fred Fulstone, 85, has grazed domestic sheep for decades. "We love this life," he said. It "should not be thrown away for 20 bighorn sheep."