Just outside Sun Oil's Prater Mountain exploratory drilling camp 8,000 feet high in Wyoming, a yellow flag flaps in the breeze, signaling that the H2S risk is low.

H2S is hydrogen sulfide, a poisonous gas that can kill a person just about as fast as he realizes an ugly sulfur smell is whisking out of the well.

There is not a bearded man in this wilderness camp. The gas mask, one for each of the 20 men here, will not seal against a bearded face so the oil men shave every day.

At other camps, says Jake Neves, the burly foreman, strangers sit high above the rig, peering patiently down through binoculars, waiting for something like a hydrogen sulfide crisis. Then the word would go out, fed through the environmentalists' pipeline to the press, that poison gases were wafting in the wilderness.

The big Texan does not tolerate the strangers above his camp. He thinks they are fools who don't understand that his technology can seal off the poisons before an eagle is felled, a friendly black bear suffocated.

Life is not easy up here. In the winter, Neves' men wear avalanche beepers and he fires explosive charges into the snow pack almost daily to keep the slides off his crew.

Merely 100,000 years ago, two giant subterranean land masses collided here, one driving deep beneath the surface of Earth and the other rising to change the form of the North American continent.

The collision shoved the Pacific coast from the fault line of the Rockies west to the fault line of San Andreas and the present shores of California, Oregon and Washington. It trapped great pools of oil and gas deep underground, far beneath the realm where dinosaurs once roamed, far below the meadows where the deer and the antelope now play.

Geologists say the underground pools, many of them three miles deep in a belt stretching from Canada to Mexico, may contain more than 8 billion barrels of oil and equal amounts of gas. This would be the greatest American oil find since Prudhoe Bay in Alaska--and it has set off a similar black-gold rush.

The primeval movement also set the stage for a thunderous collision of two other powerful forces--the environmentalists, who view human tinkering with this wonderland as almost sacrilegious, and Interior Secretary James G. Watt, who sees failure to tinker as almost unpatriotic.

In the Overthrust Belt, as this region became known, it is difficult now to say which collision has proved to be more tumultuous.

Wyoming is the epicenter of the Overthrust Belt oil boom. The boom began six years ago, moving up the old land-grant holdings of the Union Pacific Railroad from Colorado and Utah into southwestern Wyoming.

Now it has moved full thrust into the national forest on the edge of the recreational areas of Jackson Hole, the whitewater rapids of the Snake River and the grandeur of the Grand Tetons. It stands poised at the wilderness areas surrounding Yellowstone and, farther north, Glacier National Park in Montana.

Oil and gas leases have been staked out on 2.2 million acres of the 3.4 million acre Bridger-Teton National Forest, largest in the United States and the home of Neves' towering rig. Four other large national forests, their acreage claimed in similar amounts, blanket this alpine region where you almost can hear the heady echoes of John Denver's Rocky Mountain High.

It requires no imagination to hear the thunder of seismographic survey explosions as far away as downtown Jackson, a touristy little place where elk horns are woven together in archway entrances to a central park, where urban-cowboy bars make city folks think they are seeing the real thing and where rows of Lear jets are parked at the airport by rich Easterners visiting the valley's elite dude ranches.

Oil-invasion tension rides high in Jackson. The Chamber of Commerce is considering a stronger stand against oil drilling than the Sierra Club has taken. Last summer, the tires were slashed on more than 50 oil company trucks parked in town, the oil drain plugs loosened on others.

Still, it isn't true to say none of the locals likes what is happening.

A recent guest editorialist in the Casper Star-Tribune used the term "environmental extremists" 11 times in castigating the opposition to Wyoming's oil boom. Then he identified the extremists as the National Wildlife Federation, which recently called for Watt's resignation but whose membership also voted for Ronald Reagan by a margin of 2 to 1.

And Watt, who fended off protests throughout his recent tour of his home state, received far more support than opposition here.

In Gillette, where coal is king and strip mining has made the little outpost the hottest and most troubled boom town in the state, the mayor gave the interior secretary the keys to the city and told him it was a gift "to the most maligned man in the United States from the most maligned city in the United States."

Watt responded by warning Gillette that "the easterners" would come in here and strip Wyoming of its resources. It was his job, he said, to make sure that this rape and ruin didn't happen, that Wyoming got its fair reward for its contribution to the nation's "energy security."

High in the Overthrust Belt, Jake Neves reckons the old black bear that sniffs around his $11 million Sun Oil exploratory rig is the friendliest critter in these parts.

"There ain't none of the locals that like this," the foreman says in a who-could-give-a-damn Texas drawl. "I ain't saying some of 'em. There ain't none of 'em."

On the back of the dusty four-wheel-drive truck Neves uses to haul himself up rutted roads to his Rocky Mountain perch, a bumper sticker reads: "Please don't tell my folks I work in the oil patch. They still think I'm a piano player in the whorehouse."

It is Neves' way of telling the locals, Texas-style, that they can, well, stuff it.

The superintendent of the Shoshone National Forest, which borders on the eastern edge of Yellowstone, recently received 196 letters of opposition to drilling in the area. One came from John Townsley, superintendent of Yellowstone national park. Another came from Marjorie B. Gill, who lives in South Fork on private land inside the forest. Her letter read:

Oh give me no home where the seismograph roam

Probing for oil and gas.

For soon you will see, if you look carefully, that the elk have no room for their grass.

Pumps, pumps on the range, no deer and no antelope roam.

And always is heard the discouraging word,

As the wilderness turns into chrome.

The wilderness has not yet turned into chrome. This land is so big that, back East, the image of millions of acres given over to oil leases warps into the same kind of unreality that boggles people out here when they read about Washington budgets. The numbers have so many zeros they lose all meaning.

Neves' huge oil derrick has scarred just five of Bridger-Teton's 3.4 million acres. When it is all over--whether he has found an ancient oil pool miles deep or plugged up the well, dry--he will spend $1 million of Sun Oil's money covering up the scars. He will rebuild the contour of the map, plant alpine grasses and trees, and move on.

The nearest similar derrick is an Arco rig 12 miles away, far beyond high ridges and across mountain hollows. Sun's closest is 30 miles.

Still, the Overthrust boom is young. In time, it almost surely will lead to more roads in the wilderness and half-buried pipelines snaking through the forest.

In the little towns, the Stetsons are being edged out by hardhats, the denim cowboy vests by T-shirts that read, "Oil Field Trash and Proud of It."

In the woods, the change is more subtle, but with heavy overtones of high-country hostility.

Twenty-two miles up the precarious logging roads from the main highway, at the final turn to the Prater Mountain rig, Neves has planted a small white directional sign in four feet of buried cement. Except in the winter, when the snows are 12 feet deep, the sign has not stayed up more than a week. Hunters and fishermen, to whom this was a private preserve for decades, tie cable to the oil company's sign and rip it out with their trucks.

The Forest Service, which oversees most of this federal land, has its own internal troubles with the change. The government foresters, accustomed to loggers and outdoorsmen, deal less easily with the oil men. Neves says he is harassed regularly by lower-ranking rangers who, as the Texan puts it in his king-of-the-mountain way, haven't "got the word" that Washington is opening the federal forests to meet a new national need.

Higher-ranking forest officials understand the politics. But their words reveal uneasiness, too.

"I don't feel pressured to do things against my better judgment," Reid Jackson, a Bridger-Teton supervisor, recently told reporters. "At the same time, the message is loud and clear from Washington that they do not want us to throw roadblocks. They want us to be accommodating and work with the energy companies."

The boom in the Overthrust Belt, with most of the leases on government land, began long before James Watt became interior secretary. But Watt is supplying the rhetoric and the drive that fuels the boom.

Early on, Watt said his goal was "to lease every parcel of land that should be leased in the public interest." Watt also attached himself quickly to the national security rhetoric advanced by Secretary of State Alexander M. Haig Jr., who contends that the United States is in a "resource war" with the Soviet Union.

Within a month after taking office, Watt testified that he was considering opening wilderness areas to the search for strategic minerals. This left the vision here that these mountains also would be opened to relentless probing for manganese, cobalt, molybdenum and other minerals crucial to a nation virtually on a new cold war footing.

Still, no resource is more crucial than oil, with the United States warning that it may have to send men and even nuclear weapons into the far-off Persian Gulf unless it can pull the lifeblood of modern civilization out of its own continental and offshore territory.

Back home in Roby, Tex., population 784, Jake Neves was a big, tough kid when he first went to work in the oil fields in 1944. Being a roustabout made Neves king of the mountain at 16, his pockets stuffed with big bucks, his fingers stained with the black badge of Texas wealth. He was the only kid in the high school with his own car.

At 53, Neves finds life much the same. He still is king of the mountain, boss of the towering oil derrick just beneath the summit of Prater Mountain, his pockets still stuffed with oil money, enough to fly home to Texas every other week.

At Jackson airport, one of the locals smiled at him recently. "You must like it here, flying in and out so often," the friendly voice said. "What you do for a living?"

"Work in the oil patch," Neves replied, chin out.

The local turned his back and walked away without a word.

Men have known since the turn of the century that oil was buried deep in the Overthrust Belt. But in the 1940s and '50s the region became known as a "drillers' graveyard," with exploration producing almost 500 consecutive dry holes.

Then, in 1975, a small independent oil company, American Quasar Petroleum, solved the riddle that nature created 100,000 years ago. American Quasar brought in the first large well southwest of here in the corner of Utah. Since then almost 20 new fields have been discovered.

But the unraveling of the riddle also led to a modern paradox, the kind that a technological society has trouble handling.

Back in the 1930s, the great East Texas oil discovery produced 5 billion barrels and glutted the American market with so much cheap petroleum that the nation became hooked on oil like a junkie on speed.

Today, the American habit is such that the 8 billion barrels buried here eons ago is less than a two-year national supply.

The strangers sitting above the derricks look down in genuine puzzlement at others prying away at a 100,000-year-old trove that will serve no more than an 18-month need.

The men at the derricks, who have watched oil prices skyrocket as fast as gold's, look back in similar puzzlement at strangers who would wonder why they are probing miles deep into rock for a treasure worth a quarter of a trillion dollars.