Around this raw new city in the lower Don River valley 600 miles south of Moscow, the land is a quiet table of dark, plowed fields, popular windbreaks shimmering green and gold in autumnal light, and small brick houses clustered amid private orchards of harvested pear and apple trees.

There is hardly a clue that for more than four centuries, this remote edge of the Hungersteppe in southern Russia nurtured one group of the fierce Cossacks, whose warlike ways pushed czarist power eastward through Siberia, spawning legends of derring-do known today to millions in the Soviet Union.

Instead, all is aimed -- urgently so -- at the future, for it is here that the Soviets almost overnight have constructed an immense factory town to mass-produce atomic reactors critically important to boosting the Soviet Union's strained electrical power resources.

The atommash (atomic machinery) complex will complete its first reactor vessel Feb. 23, the opening day of the 26th Party Congress. Within three years, ebullient factory managers say, they will be making eight reactor vessels a year. When installed, each will add 1 million kilowatts of electricity a year to the Soviet Union and East European power grid, where demand is outstripping supply. The Soviets claim that the plant is the only reactor production line in the world, an assertion that clearly underlines the crucial role that nuclear power must play in the next 20 years if Soviet economic growth is to continue without serious energy shortages.

Although is possesses the world's most extensive coal reserves and is the world's largest oil producer, the Soviet Union's resources either are already fully committed for decades to come or are too distant and expensive to exploit in time to meet projected needs. Thus, while capitalist nations are trimming their own atomic power plans in the face of environmental questions and reduced estimates of demand, the Soviet Union will depend heavily on nuclear-generated electricity. Nuclear power accounts for about 4.5 percent of all power in the Soviet Union -- substantially less than the percentage in the United States -- and nuclear power is less important as a source of heat and light here than the wood stove. Yet by the end of the century, the Soviets hope to more than triple this percentage with atomic power plants scattered throughout European Russia, where about 75 percent of the Soviet population lives and works.

Like so many other massive projects in this country, the atommash effort shows the immense muscle a command economy can apply to a crash project and the freedom to maneuver in a country where there is no serious public criticism or opposition to government decisions.

In 1970, Volgodonsk was a backwater industrial town of 36,000 near the Tsimlyansk Reservoir, a vast manmade lake created in the postwar years when Stalin fulfilled a 250-year-old dream of Peter the Great by ordering a canal built between the Don and Volga rivers.

The project, completed in 1952, opened the landlocked Caspian Sea and the Volga River system, the nation's major commerical waterway, to the Black Sea and to world markets via the Don. When Moscow's planners settled on assembly-line reactor production to ensure future energy growth, Volgodonsk was a logical site because of its access to an ice-free water transport net.

With more than $2 billion at their disposal, builders arrived in 1976. Now, 130,000 people live in huge, high-rise apartment blocks in an area where fewer than five years ago, hunters pursued deer and duck. An additional 33,000 people will arrive each year as the atommash facility is expanded.

The work centers on an immense turquoise complex atop a small rise in the Hungersteppe at the edge of the city. According to Valery Pershin, plant general manager and deputy minister of power and electrification, each reactor, weighing 700 tons, will be fully assembled with support equipment and barged as a unit to its future site.He makes it sound very simple.

In fact, nuclear-pressurized water reactors such as atommash's are subject to intense heat, corrosion and pressure requiring design and engineering standards rare in the civilian economy. And the Soviets, like the Americans and others in Western countries with nuclear plants, have had their share of difficulties. The official press had admitted several "harmless" accidents over the years, and two Soviet-built atomic power plants in Finland have been temporarily shut down because of trouble with leaks.

"Not our work," said Pershin during a recent official visit by 60 foreign journalists. He recited safety estimates widely used in the United States before last year's Three Mile Island breakdown: "There is a possibility of one accident occuring for every 100 reactors working for 1,000 years."

Fabricating the vessels and support equipment employs 7,000 at the complex. It is work on a gargantuan scale. The Soviets -- using Italian-made heavy machinery -- shape, mill and weld seven basic sections into a single vessel of foot-thick steel standing nearly 40 feet high. Each weld must be microscopically perfect to withstand the pressures inside the reactor when controlled fission superheats water to drive turbines and generators. The Soviets check for weld imperfections four different ways, including a three-day X-ray of each weld, a process so dangerous that the X-ray chambers have doors weighing 40 tons and walls more than a yard thick to shield workers.

Pershin and his colleagues are certain that their reactors are safer than Western ones. For example, consistent with Soviet propaganda, they implied that the Three Mile Island accident was the result of capitalist corner-cutting. And they expressed no worries about disposal of radioactive wastes, a growing problem in the West. "We're a very, very big country, with plenty of places to bury things," Pershin said, dismissing the topic during a briefing.

But a rudimentary debate among party members and scientists about nuclear safety has emerged in the official press in the past year. The most significant example is an article that appeared in the September 1979 issue of Kommunist, the monthly journal of party theory.

There, Soviet nuclear expert Nikolai Dollezhal and economist Yuri Koryakin address the risks of nuclear power. They asserted that the planned construction of up to 70 large atomic plants in densely populated European Russia threatens "ecological exhaustion" by depleting ground water and land resources. While endorsing the need for nuclear power, the two warned that "safe, economic and time-tested technologies for all products of the fuel cycle" have not been perfected.

Aside from their commitment to their own massive enterprise, the atommash managers have one other reason not to concern themselves with such matters: the electricity for their complex comes from a fossil-fuel power plant nearby.