With the longest coal strike in history tying up mines east of the Mississippi, you'd think the western coal mines, which are unburdened by union troubles, would be going all out in a supersonic boom. But you'd be wrong.

Here in the Powder River basin of Wyoming, at the heart of the western coal deposit, it's business as usual. For the organized mineworkers of the East have used their enormous political power to frame environmental standards in a way that works to limit the market for western coal.

Most of the coal mined here in the Rocky Mountain states has many advantages over the coal dug up from underground in the East. It lies close to the surface and can be stripped away by enormous shovels, rather than picked out laboriously underground. Production at a good western surface mine averages 10 to 20 million tons a year as against 2 million tons at most for the best underground mines in the East.

Economics of scale and labor follow from the extensive use of machines. Productivity in the western strip mines is around 100 tons per man-shift. In the eastern underground mines, it is less than 10 tons per man-shift. Because of restive labor with a tendency to regard the wildcat strike as a right of life, moreover, productivity in the East has been dropping for a number of years.

Most important of all, western coal tends to be much freer of that noxious pollutant sulfur dixide. The amount of western coal required for a heat yield of a million BTU will also release about 0.7 pounds of sulfur dioxide - which is well within the permissible clean-air standard of 1.2 pounds per million BTU. Eastern coal leave a residue of over three pounds of sulfur per million BTU.

These advantages more than make up for some obvious deficiencies: long distances from the eastern market, the difficulty of getting railroads to do anything, and the need to replant lands laid bare by strip mining. Thus, until last year, there was an all-out boom in western coal. Virtually every major coal company got into the act. Towns like Gillette tripled their populations overnight, and the only serious constraint was the restrictive leasing policy of the Department of the Interior.

But the Clean Air Act amendments of last year took the edge off the western coal boom. The amendments require that the best available technology be applied to the burning of all coal in the United States. Thus the expensive scrubbers required to bring underground eastern coal within the 1.2-pound sulfur standard would also have to be applied to the burning of western coal, which in fact can pass the environmental test without scrubbers.

That requirement - put in by Congress and applied by the administration largely to protect coal-mine jobs in the East - wipes out the favorable differential for western coal. The western strip mines, to be sure, still sell to western markets. The Black Mesa Mine, owned by Peabody, the world's largest coal company, sells all of its output to a conglomerate of Pacific Coast utilities. The Black Thunder Mine owned by the Atlantic Richfield Company is shipping coal as far east as Green Bay, Wis., and as far south as Austin, Tex.

But the boom that would have led to truly rapid development of western coal, the boom that might have made a big dent in the country's energy problem, simply isn't on. The investors in western coal - denied their natural advantages to compete in the East , and wary of even more discriminatory environmental standards coming up - are chary about making the huge capital investments without commitments from the eastern utilities. The eastern utilities, uncertain about what new penalties will apply to western coal, are loath to sign up the long term.

"They're not beating down our doors," Charles Smith of the Black Thunder Mine says. "The western coal boom," according to Roderick Hills, chairman of the board of Peabody, "is going flat."

Saddest of all, perhaps, is the environmental consequence. Since western coal, which is well within the sulfur standard, will not be shipped east in big quantities, some eastern coal, which, when scrubbed, barely gets below the standard, will be burned. So the net result will be an increase in air pollution from coal.