For 20 seasons, the simple life was its own reward for Bob Jackson, the only resident law enforcement officer in the most remote wilderness outpost of the lower 48 states: this park's Thorofare district.

The woodwind echoes of whistling elk, the lacy imprint of grizzly bear tracks in autumn snow, the grandeur and solitude made up for the rest--the two-room cabin, the frigid outhouse, the $10,000 salary, the lack of pension and medical benefits, the wilderness scofflaws who poisoned his horses and periodically try to get him fired.

It is all part of a mystique he revels in as one of the last lawmen still chasing down outlaws on horseback. "Action Jackson" is perhaps Yellowstone's most revered and reviled back-country park ranger, poacher-stopper and champion of the grizzly bear.

These days, new threats to the wilds he patrols every summer and fall along the southern boundary of the park have left Jackson with a sense of helplessness.

The Thorofare region is under siege, he says, by unscrupulous hunters and commercial outfitters operating just outside the park's sanctuary in the adjoining Teton Wilderness, where he has no authority.

Standing at the park boundary near his cabin, he points to dozens of illegal, artificial salt licks and to signs of reckless hunting practices. He says grizzly bears, which are on the endangered species list, and elk are being lured out of the park to their deaths, and the safety of backpackers and horseback riders is in jeopardy from bullets flying into the park.

The fate of the Yellowstone bears is again in question a quarter-century after they were nearly killed off. The federal government, contending that the bears are thriving, is moving toward taking grizzlies off the endangered list.

Many wildlife scientists object, however, and their skepticism has been reinforced by Jackson's claims that the bears are vulnerable where they are supposed to be safest.

Jackson, 52, is no scientist. But mounted on his high-spirited sorrel, with the burnished stock of an old lever-action carbine poking out of its scabbard, the peace officer lends an air of authenticity to an environmental camp not usually known for its cowboy charisma.

"Those bears are a unique living link with our untamed, pioneer heritage, and they deserve a place out here," Jackson said.

Instead, a wilderness sanctuary has become "a killing zone," he said, pointing to the litter of bone fragments scattered about one of the salt licks that dot the Thorofare country. The elk are attracted to the salt and the bear prey on the elk.

As fresh grizzly tracks and well-worn game trails make clear, the animals that congregate at these baiting stations are coming out of the safety of the park, where hunting is prohibited.

Four feet deep in places, the salt craters resemble misplaced sand traps strung across miles of mountain meadows.

Salt licks change the nature of big-game hunting, eliminating what sportsmen refer to as "fair chase" and turning the experience into target practice.

Baiting wild animals with salt was first outlawed in East Africa in 1934 at the behest of big-game hunters who said the practice corrupted their sport, like shooting fish in a barrel. The practice is illegal in many states and was banned in 1990 in federal wilderness areas in the United States.

Near Yellowstone, the high cost of eliminating salt-contaminated soil is one major obstacle to enforcing the law. The U.S. Forest Service, which has jurisdiction, says that it lacks the staff to patrol the 586,000-acre Teton Wilderness during hunting season and does not have the money to remove the salt from the ground.

Also, in the Rocky Mountain West the law collides with a culture that is famously hostile to federal regulation, especially when business opportunities are at stake. And in glorious country like the Thorofare, teeming with cutthroat trout and trophy elk, business is thriving.

Most of the 250 known grizzly bear deaths in the Yellowstone region over the last 20 years have occurred at the hands of hunters just outside the park.

Typically, bears are killed during surprise encounters with hunters who are after elk, bighorn sheep or other legal prey. Although shooting a bear is illegal under the Endangered Species Act, exceptions are made in cases of self-defense. Hunters who claim self-defense are rarely charged with violating the act.

Jackson lacks the authority to probe bear deaths outside the park. Federal agencies, authorized to protect bears and prosecute people who violate the law against salting, so far have not acted on Jackson's allegations.

"Salting is clearly wrong. But tying it to bear mortalities, at least directly enough to make a case is not something anyone, including Bob, has been able to do," said Dominic Domenici, a bear management expert with the U.S. Fish and Wildlife Service, the agency responsible for enforcing the Endangered Species Act and the leading federal advocate for removing Yellowstone grizzly bears from the endangered species list.

The pressure to "delist" is coming from the states bordering Yellowstone--Wyoming, Montana and Idaho. Officials there say that grizzly bears have become too numerous. They want a hunting season reestablished. They want broader latitude to kill bears any time that they are preying on livestock, even on public land, and they want restrictions relaxed on new development, roads and mechanized recreation in bear habitat.

The size of the Yellowstone grizzly population is estimated by experts at 400 to 600, three to four times what it was when the bears were put on the endangered list.

The case for delisting presumes that the bears would be safe inside the heart of their current range--about 9,200 square miles of parkland and wilderness--where the bears would be entitled to much of the same protection they receive under the act. But skeptics such as Jackson say that the strategy effectively exiles the bears to an island of habitat too small to sustain a healthy population.

Scientists including Mark Boyce, author of a congressional study on grizzly habitat, warn that the bears' traditional food sources are declining across the Yellowstone region. Bison herds are half the size they were during the 1980s. Cutthroat trout, on which bears in southern Yellowstone feed, are being devoured by illegally introduced lake trout, and a fungus is killing the white bark pine forests that supply nuts that many bears fatten up on in the fall.

This year, Jackson closed the Thorofare cabin early, before the end of the hunting season. He said he needed to get back to his family's bison farm in Iowa, but also was glad to get away.

"I didn't come to the most remote place in the 48 states to get into the middle of a controversy. I don't like it when people don't like me. But I don't see how you can be out here in the middle of God's country if you're not going to defend it."