A cold wind from the Persian Gulf is sweeping across the rolling North Dakota prairie this spring, rattling through the scaffolding of the nation's largest construction project--the half-built Great Plains coal gasification plant--and shaking it to its very foundation.

The $2 billion plant, showpiece of a fledgling industry that was to reduce America's energy dependence on the oil sheiks, is designed to fulfill the alchemist's dream of transmuting the nation's vast coal reserves into natural gas and other synthetic fuels.

But ironically, the future of a domestic synthetic fuels industry turns out to be closely tied to the fortunes of the Organization of Petroleum Exporting Countries. It takes the soaring oil prices that are good for OPEC and bad for America to make synthetic fuels look attractive economically.

The reason becomes obvious in a visit to this labyrinthian facility, a high-technology maze of boilers, gasifiers, reactors, quenchers, exchangers and compressors that covers an area the size of 300 football fields. Producing synthetic natural gas this unnatural way clearly is neither cheap nor easy.

Hence, while the decline of oil prices over the last 18 months may be pinching the purses of OPEC, it has come close to killing off the U.S. synthetic fuels industry. One after another, projects launched with great fanfare in the 1970s have been abandoned by disenchanted U.S. energy companies.

Only two significant synthetic fuels efforts, Great Plains and a smaller oil shale project under construction in Colorado, survive.

Now, the backers of Great Plains--which has received a $2.02 billion federal loan guarantee, largest ever given any private enterprise--are warning that this project, too, is in jeopardy.

Top officials of the consortium building Great Plains have been making calls on Capitol Hill for two weeks, hinting broadly that they will pull out of the project unless additional federal assistance, such as price supports, is forthcoming.

The consortium says that because the pricing formula under which synthetic gas produced at Great Plains will be sold is tied to the price of home heating oil, which has been falling instead of rising, the partners will not earn their expected net profit of $1.2 billion in the first 10 years of operation. Instead, they face operating losses of as much as $1.8 billion.

"We simply can't withstand the cash drain of the kind that's suggested here," said Arthur Seder, chairman of American Natural Resources, lead member of the consortium.

In seeking new aid, Great Plains officials are playing on fears not only of a militant OPEC but also of the Soviet Union, claiming the project's death would send "a clear signal to OPEC and the Soviets that the United States lacks the resolve to develop a domestic synthetic fuels industry as insurance against further massive oil price increases."

The Synthetic Fuels Corp., established by the federal government after the launching of Great Plains, still plans to commit $15 billion this year to underwriting various additional synfuels projects. But Great Plains officials argue that if their project goes under, the chances that others will try are nil.

Particularly painful to builders of this plant is that, as a construction project, Great Plains is an unqualified and perhaps unprecedented success. What other recent project of this size, officials ask proudly, has been on schedule and significantly under budget?

"The management of this company has done a very fine job controlling those things that are within its control," Assistant Energy Secretary Jan W. Mares said. "It's the thing they can't control--the enormous change in expected revenues because world oil prices are so different from what was expected--that is the momentary problem."

Apart from the debate about the wisdom of building large synfuels plants, and whether today's white elephant in a time of oil glut may become the great American hope in the event of a new energy crisis, it is the sight of man transforming another of God's elements that is the most striking feature of this project.

Only a stone's throw from the fence that surrounds the plant, huge front-loading tractors are at work scooping up great chunks of coal from the rich seams of lignite that start a dozen feet below the prairie surface. When this plant is completed, 22,000 tons a day of that coal will be turned into 125 million cubic feet of natural gas.

"You know, we got started on this back in 1969," recalled Noel Mermer, chief executive of the consortium. "American Natural is primarily a gas company. After the geological data was available for 1968, we discovered that 1968 was the first year in which the United States used more gas than it found.

"So in late 1969, we did a projection of what we thought our future energy needs were going to be, and we took a look at what we thought our ability to contract for natural gas would be," Mermer said. The conclusion: "We had to rely on some other hydrocarbon source as a long-range source of gas supply."

After rejecting reliance on imported liquefied natural gas or imported oil that could be converted to gas, because it meant "relying very heavily on somebody else's control other than the United States," American Natural decided on gasifying coal.

In 1972 and 1973, it contracted for rights to 2.7 billion tons of North Dakota lignite "if and when we ever wanted to use it." The company next obtained a conditional per- mit from North Dakota to draw the huge amounts of water such a plant would require from the Missouri River.

In the aftermath of the 1973 Arab oil embargo, with oil prices rising and natural gas discoveries continuing to abate, American Natural went to Germany and negotiated for rights to the Lurgi gasification process being used in South Africa.

"We were interested in buying some technology that we felt without question would work on a commercial basis," Mermer said. "If we wanted to use it, we didn't want to struggle with proving all aspects of the technology."

In March, 1975, the company filed with federal regulators to construct and operate a coal gasification plant.

" . . . It was going to be a 250 million-cubic-foot-a-day plant, which would be equivalent to 40,000 to 45,000 barrels a day of oil," Mermer said. "That was a meaningful quantity of gas for us--roughly about an 11 percent increase in our supply."

The project's subsequent ups and downs reflect this country's on-and-off romance with developing a synfuels industry in the four decades since President Roosevelt signed a bill in 1944 promoting development of synthetic fuels from coal.

Twice in the mid-1970s, Congress became interested in synthetic fuels. But to the dismay of American Natural officials, being advised by their investment bankers "not to bet our whole company on this by trying to build the plant on our own," federal aid always seemed just a short step away.

To get the project off the drawing boards, American Natural halved the size of the proposed plant, then began taking in partners to share the financing burden.

Finally, as U.S. motorists waited in line for gasoline and oil prices redoubled amid the Iranian revolution, the administration and Congress acted. The Energy Department approved a federal loan guarantee to Great Plains in November, 1980, and in August, 1981, President Reagan made it official.

"We immediately broke ground the following day," Mermer recalled. The plant is scheduled to go into service in December, 1984.

Turning coal into high-Btu (British thermal unit) natural gas is physically impressive.

The large chunks of lignite, according to operations director Michael Mujadin, first will be crushed into eight-inch lumps. These move down a belt into a second crusher for reduction to two-inch particles before going to a coal storage building.

From the storage building, the coal goes to a screening building where pieces smaller than three-eights of an inch in diameter are separated and sent to fuel a 440-megawatt coal-fired power plant being built next door. "We will send them 8,000 tons a day," Mujadin said.

In return, each day Great Plains will receive 70 megawatts of electricity, about one-sixth of the power plant's capacity. Much of that will go into operating an oxygen plant at Great Plains. The project also will use about 4,000 gallons of water a minute to make steam.

The key step in transforming coal into gas involves taking pure gaseous oxygen, compressing it and mixing it with high-pressure steam, and feeding this through coal being dropped into the top of the 14 Lurgi gasifiers. Each of the gasifiers will be fed about 50 tons of coal an hour.

Inside the gasifiers, where the pressure will be about 430 pounds per square inch and the temperature at bottom 2,000 degrees Fahrenheit, several reactions will take place. These transform the coal into gas, leaving as a waste product a small amount of inert ash, which will be buried in the mines.

"This is an extremely efficient process," Mujadin said. " . . . What we end up producing as synthetic natural gas will have about 68 percent of the energy level that was in the coal. "If you took that same one pound of coal and burned it to generate electric power, you would get about 35 percent. So our salable energy is almost twice that."

Mujadin said the facility is even more energy-efficient than these figures indicate. All of the plant's boilers will be fired with oil and naptha produced as byproducts of the gasification process. In addition, he said, the plant also will generate as a byproduct "about 85 tons a day of salable sulfur products."

If real natural gas currently sells on average for under $3 per 1,000 cubic feet, and Great Plains would lose money selling synthetic gas at the $6 it could charge today, why proceed?

"We tend to get very sanguine about things," Mermer said, shaking his head sadly. "We forget the gas station lines. We forget the embargo. But " . . . if you look at the Middle Eastern situation today, who could say: 'No. Don't build this plant. We are going to have a 25-year reliable source of energy in the Middle East'? . . .

"I think the short-term events do nothing but underscore the instability and volatility of world energy markets, and our vulnerability to future energy disruptions," Mermer said. "I think projects like this will help unmortgage our future." CAPTION: Picture, Backers of the half-built Great Plains coal gasification plant, which has already received a $2.02 billion federal loan guarantee, says more government money is needed. Great Plains Gasification Associates photo