July's first rain came in the evening, rolling in waves across the sky as the sun dawdled on the vast Kazakhstan horizon.

It came just in time for Andrei Andreivich Rimmer, director of the Erkenshilikski state farm, 120 miles north of here. The month-long string of hot, dry days had him worried, and he had begun to dread another drought like last year's.

Earlier in the day, asked what Moscow authorities could do to improve life on the state farm, with its 260,000 acres and 5,000 inhabitants, Rimmer, a large, jovial man of German descent, boiled it down to one word. "Rain," he said, and laughed, wiping the sweat at the back of his neck.

Early July is a critical time for the spring wheat crop in this arid region of the Soviet Union. It is when the young plants approach the reproductive or "heading" stage. No rain means a crippled, puny sprout; rain at the key moment means a good harvest, an event of importance not only to the Soviet Union but to countries such as the United States that sell it grain.

The drought here last year contributed to what has been estimated as the Soviet Union's second worst harvest since 1975. The Kazakhstan harvest -- 17.5 million tons -- was half what it was in the bumper year of 1979.

This year, the same dry spell that had Rimmer worried on his central Kazakhstan state farm lowered the U.S. Department of Agriculture estimates of the 1985 Soviet grain harvest from 195 million to 190 million tons. This, in turn, has put the estimates for Soviet grain imports in 1985-86 at 37 million tons.

Kazakhstan, a huge republic stretching from the tip of Mongolia to the Caspian Sea along the Soviet Union's border with China, lies at the center of Moscow's plans and hopes for its grain crop.

In recent years, it has contributed only about 10 to 13 percent of the total Soviet grain crop, ranking third after the Russian Federation and the Ukraine. Its climate, while typical of the huge grain-growing area east of the Ural Mountains, cannot be taken as a bellwether. As one local specialist said, rain here can drench one wheat field without touching the one next door.

Still, Kazakhstan is a critical region: A good crop here is essential if the Soviet Union is to come close to meeting its agricultural goals. Bumper crops in Kazakhstan in 1972 and 1979 saved the country from disastrous years.

Kazakhstan is also a powerful symbol in the history and mythology of Soviet agriculture. It was here that Nikita Khrushchev launched the "virgin lands" campaign of the 1950s, one of the country's most ambitious and arguably successful "hero" projects.

The first trainloads of Young Communist League, or Komsomol, members arrived here in March 1954, ready to do their patriotic duty and transform acres of barren steppes into wheat fields. Of the 104 million acres of virgin lands in the program, 62 million were in Kazakhstan.

This city, which still has the baked, dusty feel of a frontier town, was then known as Akmolinsk. Its name was changed to Tselinograd in 1961 for the tselina, the Russian word for virgin land.

The tselina changed the face of the republic. Kazakhstan's population of 6 million in 1941 more than doubled by 1970 and now numbers more than 15 million. In three years, the amount of arable land increased by 49 million acres. The reclaimed lands produce 64 percent of the republic's grain, 38 percent of its meat and 49 percent of its milk.

In the early years, the virgin lands program was considered by many to be a risky investment, a squandering of land and labor, one of Khrushchev's impulsive schemes.

Leonid Brezhnev, who was to succeed Khrushchev as Soviet leader in 1964, was his local political lieutenant in Kazakhstan during the virgin lands campaign, serving as the republic's second, then first, party secretary in the mid-1950s.

Brezhnev survived his association with the volatile Kazakhstan grain crop, and one of the main squares in the Kazakh capital of Alma-Ata is named after him.

Khrushchev was not so lucky. A catastrophic harvest in 1963, which led to enormous grain purchases abroad, was considered one of the several causes leading to his downfall.

Here where his legacy is felt daily, memories of Khrushchev are ambivalent.

"He was a good man," said Rimmer, who became state farm director in 1965. "After all, everyone makes mistakes."

Aleksandr Beraev, head of the All-Union Grain Institute at Shortandy, personally suffered from Khrushchev's impetuosity and wrath. Beraev pioneered the concept of subsurface tillage here, a method of plowing designed to save the fragile topsoil of the steppes from wind erosion, and advocated letting land lie fallow periodically.

Khrushchev was more of a traditionalist and, after an argument with Beraev, tried to force the agronomist out of his job. The local Communist Party committee, however, rebelled in a rare display of autonomy and Beraev survived.

Still in the job, Beraev is now a revered figure in Kazakhstan. Of Khrushchev, he said: "He should be appreciated because he was able to mobilize the country, but unfortunately it was for something for which the country was not yet ready."

The virgin lands program was the most extreme of the Soviet Union's efforts to offset its agricultural liabilities by "extensive" development, or land reclamation.

In recent years the byword in agriculture is intensive development, a theme favored by new Soviet leader Mikhail Gorbachev, who was agriculture minister for almost six years. Instead of expanding acreage, the aim is to improve production through more scientific methods, better conservation and greater incentives to workers on collective and state-owned farms.

Despite this new thrust, land reclamation still plays a key role in Kazakhstan's agriculture future. During the next five-year plan, the republic expects to reclaim almost 10 million acres of salinized soil. This land, distributed in northern Kazakhstan among land already under cultivation, will be costly to reclaim. It requires special equipment and chemicals.

Kazakhstan, like other southern republics, also has hopes for the ambitious water diversion schemes still under study in the Soviet Union. Plans to divert water from north-flowing rivers to the sun-baked south would greatly benefit the republic's western half, raising production yields.

But in the end, the region's harsh climate -- cold winters, hot summers and whipping winds -- are a natural limit to the republic's potential. The average rainfall in central Kazakhstan is between 16 and 32 inches a year, far less than what the North American corn belt expects each year.

Soviet agricultural experts, sensitive to recurring farm failures, always are quick to point out the climatic problem.

But there is also a growing impatience with the tendency to blame the weather for everything. The fact is that in the past 10 years, the grain crop in Kazakhstan, averaged to cancel out the effects of particularly bad years, has actually declined from an average of 27.5 million tons in the years between 1976 and 1980 to an average of 20.6 million tons in the years 1981-84.

Kazakhstan, like other farms areas of the Soviet Union, has other chronic problems that are not mentioned by local officials. For instance, the republic ranks 15th of the 15 Soviet republics in per acre use of mineral fertilizer.

As elsewhere, farmers here have difficulty getting other chemicals, pesticides and spare parts.

There is also waste and spoilage of harvested grain because of delays in moving it to the silos, sometimes located 50 miles from the farms. A local official put the amount of grain lost after harvest at 5 percent in the republic, but travelers have been told privately that in one district, the amount is as much as 30 percent, again because of the distances from farm to silo.

In an article in March, a Soviet agricultural newspaper urged new attention to the problem of increasing grain production, noting that yields were far below target figures.

The crusade conducted by Beraev during the Khrushchev years has borne results. Most farms now use subsurface tillage here, and the amount of land left to lie fallow is increasing.

During the winter, snow is trapped by hardy bushes planted along the fields. It is piled in rows to catch and retain as much moisture as possible during the thaw.

So far this year, they say the crop looks good. In fields that stretch as far as the eye can see, the wheat is about a foot and a half high, green and healthy.

"It's pretty clean, maybe average," said Mexlix Suleimenov, an agronomist at the Shortandy institute. "But right now, it depends on the rain. It is a critical time."