With the return of summer to the vast northern lands of Russia, the United States has begun anew to peer intently at the fields and furrows of Soviet croplands in hopes of estimating accurately the eventual harvest.

Using satellites and ground survey teams, the United States assembles information on soil moisture, germination, plant growth and other critical factors to arrive at the estimate.

It is sensitive business, underscoring the interdependence, however uneasy, that has evolved in recent years with its super-abundant farms and the Soviet Union with its struggling, problem-ridden agriculture.

The Soviets don't like satellites looking down from above or expert foreign agronomists walking their fields, seeking out problems. "They like to lead from the assumption of self-sufficiency," said one Western expert.

But the Soviet Union is only marginally self-sufficient in feed and fodder and its shortcomings in recent years have forced it to spend hard currency in the West-principally in the United States-to make up the differences as it struggles to increase meat supplies for its millions. Under its current five-year plan, per capita consumption of meat and meat products is to reach 165 pounds from the current 121 pounds. The only way it can achieve the needed increase in its livestock and poultry is to supplement its own harvests with imports.

The bilateral trade with the United States is more a function of necessity than of detente, although the easier relations between Moscow and Washington several years ago surely added impetus to the signing of the agreement. "The soviets like to be totally free to buy when they choose," said one source.

The 1975 agreement requires the Soviet to purchase a minimum 6 million metric tons of grain annually from the United States and to notify Washington in advance if it needs more than 8 million tons. The agreement, which will run through the harvest of 1981, will add billions to U.S.-Soviet trade totals, regardless of the state of political relations.

The trade agreement grew out of the disastrous 1972 Russian harvest when unforeseen, Massive Soviet purchases of American grain triggered surprise shortages and spiraling consumer costs for bread, meat and poultry in the United States.

The 1972 difficulties emphasized the U. S. need for crop information from the Soviets. "The more information the West has on crop production, the better it can plan for major demands from here," a source said. "The ideal situation is to get requirements estimates ahead." At the same time, too much information could place the Soviets at a disadvantage in the world market, where prices could be rise on accurate advance word of a Soviet harvest short fall. The Soviets, who are notoriously tough businessmen, are not forthcoming about harvest shortcomings.

U. S. crop experts for a number of years have traveled in old Russia, west of the Urals, inspecting grainlands periodically through the growing seasons. "They've been accepted by the Soviets with the full knowledge of why they are there," one Western expert said. "The survey team - an agronomist, an experienced farmer and an official of the Agriculture Department's crop reporting service - are accompanied, constantly by Soviet authorities on their car travels through the region, which may last two or three weeks.

One such group now is coming to the end of its survey of old Russia and will return home over the July 4 weekend. "The information they will be carrying is considered so sensitive to world commodity markets that it will be assessed thoroughly in Washington before any of it is made public, despite the fact that the growing season has many weeks to go.

"Things look good now," one expert observer said. The Soviet press, while saying there have been sowing difficulties generally in the country due to a cold, wet spring, have reported a good start on most crops and higher than normal soil moisture east of the Urals. But much can happen between no and harvest time in a country which has had bizarre swings in harvests in recent years.

American surveys of European Soviet Union have been accurate within a few percentage points of the actual harvest reported by the Soviets. Last year, for example, the U. S. forecast in the Ukraine, traditional breadbasket of the Soviet Union, was within 3 per cent of the actual harvest.

Nevertheless, the Department of Agriculture and the Central Intelligence Agency overestimated the total Soviet grain harvest by 19 million metric tons, at 215 million when actually it was about 195.5 million. The discrepancy was not known until Soviet President Leonid Brezhnev announced the harvest results at a Kremlin rally marking the 60th anniversary of th Bolshevik revolution last November.

The United States was caught by surprise in part because it has had only limited access to the "new lands," where 89 million acres is under graintillage in Kazakhstan and the Southern Urals. Large portions of this territory is off-limits to foreigners.

These lands, subject to frequent fierce summer drought and harvest-time rain that rots crops, are the key to Soviet agricultural sufficiency. The government has earmarked billions of rubles for better farm machinery and more fertilizers in the current five-year plan, so far with indifferent results. A U. S. survey team will be shown selected sites there soon, and what they see may help the United States get a better picture of overall harvest prospects.

During his visit here last month, Agriculture Secretary Bob Bergland had only limited success to expand U. S. access to Soviet crop information and growing lands. Grain purchases by the Soviet Union last year to make up its harvest shortfall helped somewhat to deplete the immense wheat and corn surpluses that had brought U. S. crop prices to a five-year last summer because of slack demand abroad.

Bergland succeeded in setting up a special joint committee that may help to reduce the secrecy of Russian harvests. The current preliminary U. S. Agriculture department forecast is for a Soviet harvest of better than 205 million metric tons. But it may be months before anyone-other than the Soviets-knows how accurate that is.