In what were once desert wastelands east of this prospering market town, a new breed of Saudi farmers is working to make the kingdom self-sufficient in food and themselves millionaires.

Commoners and princes alike, they include businessmen and young Saudis educated abroad, responding to an opportunity to make a killing in the fastest growing sector of the economy but also to a patriotic appeal from King Fahd for self-sufficiency in basic foods.

But to make the Arabian desert bloom, Saudi Arabia is spending vast amounts of money, much of it in subsidies that are enriching the farmers. U.S. Secretary of Agriculture John R. Block got into an argument with the Saudi agriculture minister about it last year, and an awe-struck American farm expert, after studying the generous subsidies for irrigation, observed: "You could sprinkle Perrier water on that wheat and still make money."

"We are in the process of reclaiming the desert," said youthful Prince Muqrin, the governor of Hail. He is a brother of Fahd and an active tractor-driving farmer himself.

"We call it 'food security,' not 'self-sufficiency,' " he said in an interview. But, he added, "it's becoming now a new way of life, farming; success breeds success."

Kadhim A. Khalil, the American-educated Iraqi manager of the biggest farming project in the area -- 460 miles northwest of the Saudi capital on the edge of the Nafud Desert -- explained the phenomenon another way.

The Saudis, he said, "were importing 49 percent of their food requirements. This statistic killed everybody. With all this money, we might as well invest in the country, they said."

And so they have -- billions.

Huge tracts of land around Hail and in neighboring Qassim Province to the south have become the kingdom's new "wheat belt," with a production that last month won Saudi Arabia a certificate of honor from the U.N. Food and Agricultural Organization for achieving self-sufficiency in wheat, poultry and dairy products.

The Saudi wheat harvest has shot up from only a few thousand tons in 1977 to 1.3 million this year and a projected 1.9 million next -- twice the country's own needs. Grain elevators are overflowing. Nowhere else in the Arab world is such rapid progress being made in farming.

This performance provides a fascinating example of the power of money in Saudi Arabia and the way it can be used to achieve spectacular results even against the odds of nature in the barren Arabian desert.

The Saudi farming policy, however, has been criticized sharply by some outsiders because the government has aided it with huge subsidies and because vast quantities of the country's limited underground water resources are rapidly being used up.

As Khalil explains it, one cannot go wrong investing in agriculture here -- mainly because the government assures the farmers that it will buy their wheat for $1,000 a ton -- five to six times the world price.

The government subsidy to support the high prices paid wheat farmers amounted to about $1 billion this year, and $286 million more was spent to subsidize farm machinery, pumps and feed.

Since 1980, the government has given out $2.3 billion in interest-free loans and service. It has invested $12 billion to develop water resources and $1 billion for grain storage facilities, according to a local press report.

Block ruffled feathers during a visit here in May 1983, when he told the Saudis publicly he thought they were "crazy" to spend so much money on producing wheat when they could buy it from "a reliable partner" like the United States at a fraction of their own production cost. He even offered a U.S. guarantee of food supplies if they would end "their thrust to self-sufficiency at any cost."

Saudi Agricultural Minister Abdulrahman Ashaikh replied that his country did not need Block's "advice" and that for reasons of "patriotism" and "food security" it would continue spending its billions on developing farming.

"We would also tell him," Ashaikh retorted, "that we are doing exactly as his country is doing by spending not tens or hundreds but billions of dollars in order to build a sector that would rid them of our oil."

The way Saudi Arabia has achieved self-sufficiency in wheat can be seen at the three-year-old farm of Hadco, the Hail Agricultural Development Co., located 67 miles southeast of Hail and atop a large underground aquifer.

The company, one of the country's biggest, was set up in 1981 by 27 Saudis who put up $23 million of the total $86 million capital with the rest raised by selling shares to 57,023 other Saudis, Khalil said.

The "farm" is a 22-mile-long stretch of former grazing land along the Hail-Buraidah road. It covers 80,000 acres and produced 112,000 tons of wheat this year. This harvest was made possible, according to Khalil, by the "pivot method" of irrigation and 10,000 tons of fertilizer.

The pivots are 400-yard-long wheel-driven sprinklers mounted on booms that creep in a circle, covering about 125 acres in a rotation. Hadco used 300 U.S.-made pivots this year to water 37,500 acres.

There are several question marks over the Saudi agricultural miracle, the biggest being whether the government in the present recession can continue to pay the high subsidy. There are reports that it will be reduced starting next year, or switched to another grain, like barley or alfalfa, to encourage farmers to rotate crops.

Another question is whether water resources will hold out. Already, the water table is dropping rapidly in many areas -- 12 yards since 1970 in some parts of the Eastern Province.

Khalil's Saudi deputy, Aqeel Ogla, is philosophical. "We have plenty of water still," he said. "It's very hard to just leave it there and not use it." -- David B. Ottaway