When Ronald Reagan comes to Washington as president, his inaugural procession will include the sheriff's posse on matched palominos that television viewers remember from Tournament of Roses parades. The riders may be getting heavy in the saddle, but the horses will be splendid and the tack will be Hollywood Charro -- every saddle, headstall and martingale crusted with silver to the amount of $25,000 per horse.

The posse's presence will emphasize that Reagan comes as a Westerner, backed by something called the Solid West (he received 60 percent of the vote in the mountain states), at a time when the West is growing explosively in population and economic potency, acquiring headache proportional to its economic spree and seeking political power to match its importance to the American future.

Western assertiveness stems from many things -- the rush to the Sun Belt and the no-less-important escape to the open spaces and the unhassled life; the accelerating exploitation of coal in Montana, Wyoming, North Dakota, Colorado, Utah and New Mexico, and of uranium in New Mexico and Utah; the stepped-up deep drilling for oil and gas in the Overthrust Belt that runs from Arizona to Montana; the Department of Energy's $20 billion mandate to promote coal gasification and oil shale plants in their inevitable western locations, and proposals for enormous power projects in Wyoming, Montana, Colorado and Utah with accompanying transmission lines, slurry lines and coal-hauling railroads.

There also is the Air Force's MX Missile system, the largest construction job ever planned in the United States, slated for the Utah-Nevada desert at an estimated cost of $34 billion that critics say will be three times that; the hectic growth of Denver, Phoenix, Tucson, Salt Lake City, Albuquerque, Las Vegas and dozen of smaller places, and the imminent emergence of Los Angeles as the second city of the country.

Pursuing opportunity and amenity, population flows from Northeast and Mideast to South and West. Pursuing resources, big capital and some aspects of big government flow to the mountain West, where they encounter special conditions and create special problems.

The mountain West is new, raw, thinly settled, blessed with scenery and minerals and inhibited by an intractable deficiency of water. Histically, its resources have been plundered, not developed. Beaver, gold and silver, grass and timber were successivley exposed to the economics of liquidation, whose profits did not remain to enrich the local life.

Settlement, thin and poor, dug in and made its hard adaptations among the leftovers of the raiders and, through a century and more, there has developed in the West a ranching and farming civilization at once humble and touched with glory, practical and myth-bound, something made up about equally of deprivation, hard work, mule-headedness, pride, freedom, self-sufficiency and illusion.

Isolated, economically exploited, culturally ignored and politically impotent, the West always had its nabobs, but even small Westerners felt lucky. Their life was a dance at which the federal government, owning nearly half of the territory west of the 100th meridian, called some of the tunes but also paid the band and tried to police against crashers.

It was a good dance, neighborly, strenuous, spacious, democratic, mobile and satisfying. Few Americans love their life or their region as rural Westerners do.

Into this oasis civilization of ranches, dry farms, irrigated farms, county towns, small provincial capitals and vast public open spaces the 1970s projected new raids of unpecedented speed, power, extensiveness and potential duration.

Coal seams and oil shale deposits are far less localized than placers and will not be exhuasted so fast. Streams used up by industries, slurry lines or new cities will not be there as they were after extermination of the beaver. Strip-mine spoils do not head over with native grasses; some experts say they can never be reclaimed. Springs go dry when draglines rip up the aquifers, and some aquifers, notably the Snake River Aquifer in Idaho, are contaminated with atomic wastes.

Water tables throughout the West are pumped down and going lower. Air that once fizzed in lungs and sharpened distances darkens and lies in a sour, brown cloud.

While paychecks fatten and businesses spring up to service thousands of temporary Westerners, many stable communities are swamped.

Energy conglomerates rush to complete new skyscraper headquarters in Denver, and construction workers in Evanston, Wyo., make $1,000 to $1,500 a week, but not everybody wants to sell out to the boom.

Ranchers in the Billings area have been known to run off energy company representatives with shotguns, and angry protests rise from Westerners when some federal agency proposes using public land in their area as a dump for surplus nerve gas or atomic wastes or as a playground for the MX missile or as a sacrifice area for production of energy to be used elsewhere.

The Intermountain Power Project in the western Utah desert will be the world's largest, generating as much electricity in a day as all of Utah uses in a year. It will destroy the life of that desert valley.

The West is not as solidly pro development as the election made it appear.

Does Reagan represent the West and, if so, what West? He owns a ranchette and a couple of hundred head of tax-deductible cows, and he if often photographed on a horse. Is he a Westerner such as LBJ, with knowledge of an interest in western problems, or one such as Richard Nixon, whose priorities were elsewhere and who was almost totally indifferent to problems of the region? How much does Mr. Reagan actually know about the West?

All of Reagan's experience has been in California which, if it is West, is West with a difference. Except along its northern coast, it does suffer from the chronic western water shortage and in many places has already overdrawn its supply. It is 45.5 percent owned by the Federal government. It is big, spacious, scenic and well endowed. It even suffers to some degree from the western inferiority complex in cultural matters and to that degree resents Eastern condescension. In other ways, it is not the West at all.

With an economy that outperforms that of most nations, California cannot be called undeveloped. Much of its capital originates and stays at home. Nor is it politically impotent.

Instead of being part of the victim West, ringed with predators, it is seen by its neighbors as one of the principal predators, especially in its insatiable appetite for other people's water. It has undergone its boom well ahead of the rest of the West and now disperses its overflow population, its capital and its branch plants throughout the neighboring states.

If Reagan is a slightly ersatz Westerner, he has tried to sound like an authentic one of a certain kind. During the campaign he expressed and, after the campaign reiterated, his support for the Sagebrush Rebellion, that union of stock growers and politicians who furiously resent all. federal regulation and want all unappropriated public lands turned over to states that contain them.

Reagan's closest adviser on western matters probably is Sen. Paul Laxalt of Nevada, one of the fomenters of the Sagebrush Rebellion.

Another long-term friend is Sen. S. I. Hayakawa of California, who would like to give Redwood National Park to the loggers. James Watt, Reagan's choice as Secretary of the Interior, probably was selected by Laxalt as the first step in his promised general housecleaning of Interior. Watt expresses Reagan's probable intentions as bluntly as a kick in the shins.

Unlike Sagebrush hard-liners, Watt appears not to expect a complete turnover of the public domain to the states, and that may be significant. The Mountain States Legal Foundation, for which Watt has worked for several years, was created by Adolph Coors and some of the development corporations that encircle the West like wolves around a crippled buffalo. Those companies have supported the rebellion with some caution, perhaps because, if Interior can be headed only by a secretary friendly to development, then a single set of federal regulations would be easier to deal with than a dozen diverse state codes.

If Reagan seems not quite whole-heartedly in favor of states rights or recession, he is unambiguously antifed and antiregulation. One thing that must have recommended Watt to him is that Watt has made his recent career bucking what Reagan called "environmental extremists" and suing federal agencies in order to have environmental regulations relaxed and wilderness and wilderness-study areas opened to oil and mineral exploration.

Nobody expects Watt to invoke the Clean Air Act to protect a national aprk from a nearby power plant's plume blight. Also, environmentalists glumly remind themselves, the Clean Air Act itself is up for review this year -- by the Reagan Congress.

Eastern states withering under acid rain might rally to help save the Clear Air Act, but they are less certain supporters of such western-focused legislation as the Federal Land Policy and Management Act (the so-called BLM Organic Act) or even the Strip Mining Act, both of which will be targeted by powerful interests in the West."

Development is foremost in the Reagan plans for the West. The environment will take its chances, and protective federal legislation will be weakened even if the extreme claims of the Sagebrush Rebellion come to nothing. And one kind of West -- the only West with a continuous and renewable way of life, the West that is a partnership of ranching and farming valleys, market towns, limited industry, federally developed water and federally protected open space -- is not mentioned at all.

Does Reagan take his stance out of knowledge and conviction? Does he sincerely believe in unlimited free enterprise and the economics of liquidation?

If he thinks like a rancher, does he think like a big rancher, which is one of the breeds of special privilege, or like a family rancher, which is another kind, or like a tax-writeoff rancher, still another kind? Is he a Lone Ranger riding out to right the wrongs of people oppressed by Washington's absentee landlords, or one of a posse on the way to rub out the nesters and preserve the range for the men on horseback?

Is he, as some fear, the instrument of interests more knowing and far less affable than himself? Or is he a role, a figure in a parade, an empty white Stetson on a $10,000 horse with a $25,000 saddle?

The answers await the event. But during the campaign, while cementing his alliance with the Sagebrush rebels, Reagan asked an astonishing question. Why, he said indignantly, is there so much more public land in the West than in the East? Why this unfair bondage to Washington? He promised to appoint a presidential commission to get him the answer.

The question demonstrated whom he had been listening to, but it did not add to his stature as a student of western affairs. Only a man who knew literally nothing about western history could have asked it seriously.

One reason there is so much more public land in the West than in the rest of the country is that, reviewing its own history of waste and spoliation, the nation got smart and put away large amounts of national forest and national park land while it was still available.

Another reason is that -- despite grants to railroads, states and educational institutions, veterans' scrip, Homestead Act, Desert Land Act, Timber and Stone Act and considerable grafting under all of these -- the nation was unable to dispose of the remainder.

In 1878, Maj. John Wesley Powell submitted to Congress his seminal "Report on the Lands of the Arid Region," in whose first three chapters he said more truth about the West than anyone before him or many since.

Powell defined the beginning of the West at the 100th meridian, beyond which agriculture unaided by irrigation was chancy or impossible. He pointed out that 160-acre homesteads and the rectangular surveys that defined them worked only east of the 100th meridian, that there was water for only a fraction of the land, that the water was distributed erratically so that cattle companies often preempted a princely range of publicly-owned land by controlling the water sources and that if farmers were to avoid family disaster and serious damage to the land there had to be reservoirs and canals developed cooperatively.

If he had been listened to, the West would be more securely settled, and the federal government would be less of a presence there. But the old patterns of settlement went on.

There was a chance in 1888, when Powell was put in charge of an irrigation survey to select reservoir sites and designate irrigable, hence farmable, lands. But Sen. William M. Stewart of Nevada, who had pushed the survey, found that he had inadvertently closed the entire public domain to entry.

When Powell insisted on doing the survey thoroughly instead of hastily, Stewart undid the legislation in 1892, breaking Powell by helping to cut the Geological Survey budget.

The public domain returned to the old pattern of homesteader failure, water monopoly and land frauds, with some substantial federal withdrawals and, after 1902, heavy infusions of federal dollars for reclamation projects.

The policy of disposal actually began to end with the reservation of Yellowstone National Park in 1872.

In 1934, with the Taylor Grazing Act, the federal government acknowledged permanent ownership and management and, in 1936, the Bureau of Land Management replaced the Land Office. The Taylor Grazing Act began the rescue of public lands from neglect and abuse, but the BLM had no teeth, and local grazing districts, encouraged by another senator from Nevada, Pat McCarran, dominated it.

Now still a third Nevada senator, Laxalt, rises to defend the unlimited, unregulated grazing privilege and advocates what amounts to a policy of secession, charging that absentee landlordism and bureaucratic meddling violate the "equal footing" of the public-lands states and are interfering with individual initiative.

They certainly are, or should be. Since 1872, they have been trying to save the West from just such personal initiative as brought it to the Dust Bowl.

To the land management bureaus -- the National Park Service, the National Forest Service and, to a lesser extent, the BLM -- we owe the West's continued spaciousness, wilderness areas, improving ranges, relatively healthy watersheds and the privilege citizens and tourists share in the marvelous open country around oasis valleys, towns and even major cities.

Also, again contrary to Sagebrush contentions, the states have benefited, not lost, by federal stewardship. They all get back, in mineral- and grazing-lease money and money in lieu of taxes, a great deal more than they could possibly make from those public lands, unless they destroyed the lands in the process.

Does Reagan know these things or grant them importance? Does he really back the secessionist position of the Sagebrush Rebellion and want to turn the public domain that belongs to all citizens of the country over to local governments dominated by precisely the rugged individualists who nearly ruined the land earlier?

Does he know about water in the West? President Carter manifestly did not and made several moves that cost him support in the area. Or does Reagan believe that individual initiative, or science or something will create water as it is needed?

When Maj. Powell addressed an irrigation congress in Los Angeles in 1893 and found it full of boosterism and extravagant expectations, he threw away his prepared speech and warned bluntly that the delegates were preparing an inheritance of trouble because there was water enough in the West to serve only about 20 percent of the land.

Powell was booed, as oil-shale people and slurry-line people and MX missile people, might boo him, but the stricture is still valid. Water cannot be created, only retarded, impounded, redistributed, mined and sometimes recycled. When you come to the end of your supply, you may find yourself, like Los Angeles, stealing it from the Owens Valley or borrowing it from Arizona's share of the Colorado River or creating canals to pipe it away from the San Joaquin delta, at whatever cost to the areas you take it from.

The MX missile, for construction and operation, would use 172 billion gallons of water -- in the driest heart of the arid West. The Air Force describes the problem as difficult but manageable, a judgment that the governors of Utah and Nevada might describe as hopeful but insane.

Stated in simplest terms, the West is being fought for by a new, powerful wave of raiders and those who would preserve it as a place capable of some sort of visible, continuing, renewable life.

The Sagebrush Rebels, except insofar as they plan turning the West's resources over to corporate exploitation, are merely noisy and absurd and dominated by a myth of rugged individualism that never had a basis in fact. Cooperation, not individualism, made the West.

The energy companies with their enormous capital power are neither noisy nor absurd. They are perfectly logical, knowing and efficient. They can make the West give up vast riches, especially in energy. But they may well kill it in the process.

The more that James Watt's policies succeed, the less open space the West will provide for natives or tourists, the less unhassled life will be discoverable by those seeking it, the dirtier the air will be, the scarcer the water, the lower and more impure the groundwater tables, the less irrigated farming, the less ranching, the less grass, the less of the West itself as we have known it.

Most westerners would not want the West sacrificed, even at a high price. Raiders characteristically have never cared and do not now. And it does look as if Reagan is riding with the posse.

Whether he is a real gun hand or only a figurehead, whether he acts out of ignorance, indifference or political expediency, it looks to a lot of westerners as if he has decided to throw the West to the raiders and Sagebrush rebels of the right wing.