Despite U.S. fears that the Falkland Islands crisis could push Argentina closer to the Soviet Union, Moscow's grain buyers apparently are trying to use the situation to obtain Argentine corn at bargain prices and thereby shave tens of millions of dollars off the Kremlin's 1982 food import bill.

The Soviet grain trading agency has not signed any new contracts to buy Argentine corn since March 22 and so far has committed itself to buy less than half of the 1982 Argentine grain surplus, far less than in 1981, according to official and private sources.

The upshot, the sources say, is that the price at which Argentine grain is being offered in world markets in Geneva and Rotterdam has been falling fast and traders are offering it this week at $8 to $12 a ton below the price of U.S. corn, currently about $120 a ton.

One American official predicted yesterday that the Soviet government eventually will commit itself to major new orders--but not until the price has been driven down to bargain levels.

"This is a Russian maneuver," said an American official. "They want to make the Argentines sweat a little bit and get the U.S. grain traders all lathered up about selling more to the Russians. But when the price gets low enough you will see the Russians going back to the Argentines for more."

Grain trade sources say the maneuver is coming at a time when the Soviet government has maximum leverage over Argentina and, at the same time, has strong financial incentives to press home its commercial advantage.

Millions of tons of corn and sorghum from the Southern Hemisphere's spring harvest are now moving off Argentine farms to the grain ports of Rosario and Buenos Aires, where storage capacity is limited.

Normally the international grain companies that dominate the Argentine export business could quickly find buyers other than the Soviet Union for this crop. But the conflict raging in the waters off Argentina has caused unusual problems. U.S. officials report that Lloyd's of London has stopped issuing war risk insurance for merchant vessels, effective yesterday. And many shipowners have been unwilling to send grain vessels to Buenos Aires even with insurance, except in return for huge premiums. These factors have discouraged potential customers and forced big markdowns in Argentine grain prices.

The Soviet Union is apparently in no hurry to come to the Argentines' aid, officials said.

Some 2.8 million tons of freshly harvested wheat was shipped to Russia from the port of Bahia Blanca earlier this year--about the same as last year. But so far only 4 million tons of corn and sorghum have been contracted for, compared with 11 million tons shipped in 1981, and unless there are new contracts the shipments will come to a halt in mid-June.

David Lacroze, head of the Argentine National Grain Board, will go to Moscow early in June to discuss the situation.

The continued uncertainty about grain sales could serve as a Soviet bargaining chip in negotiations aimed at establishing broader political ties, arms sales agreements and other links with the Argentines.

However, this possibility was downplayed yesterday by some U.S. officials and traders who said they believed the Soviet Union was mainly interested in financial bargains.

It has already sold large quantities of gold to pay for food imports and is facing temporary shortages of cash to pay for imports. Adding to the financial pressures is West European banks' caution about extending new credits to any East European countries since Poland fell into arrears on its foreign debt.

The Argentine government reportedly has informed the Soviets that its own financial problems and its need to finance the war rule out offering credits for grain buying.

In 1980, when President Carter imposed a partial embargo on U.S. grain sales to Russia, the Soviets were forced to pay premium prices for Argentine grain to cover their needs.

Today, the U.S. embargo has been lifted and the Reagan administration has authorized American sales of up to 23 million tons, a fact that takes the pressure off the Soviets as they seek to procure some 40 million tons of grain from abroad this year.