Moscow — The Soviet Union, with a little help from Washington, has been moving to blunt the effect of any renewed US grain sanctions.
President Reagan, in announcing restrictions on trade with the Soviets Dec. 29, said ''further steps may be necessary'' in protest over the situation in Poland. This was widely taken by diplomats here as an indication he was considering new grain sanctions at a time when the Soviets are having to cope with the effects of their third poor harvest in a row.
Foreign experts here remain divided on just how badly the Soviets were hurt by former President Jimmy Carter's restrictions on grain sales following Moscow's December 1979 intervention in Afghanistan.
But the consensus view is that, although the Kremlin managed largely to offset the cutback in US deliveries by buying elsewhere, the result was somewhat less imported grain that was of lower quality and purchased at a higher total cost than the Soviets might otherwise have managed.
Some diplomats add that the Carter-era restrictions, lifted by Mr. Reagan, also threw off Soviet port operation and generally complicated delivery of grain and other imports.
An early reimposition of US grain restrictions could have similar effects, Western diplomats here say. Since the beginning of the current US-Soviet ''grain year'' in October, the Soviets have contracted for some 11 million tons of American grain. More than half of this remains to be delivered.
But generally, the diplomats say, the Soviets appear in much better shape to cope with the short-term effects of an American embargo than they were two years ago.
First of all, Western sources here say Moscow appears likely to import less foreign grain than some US officials had thought. Official US estimates -- geared to the international grain year of July to June -- said the Soviets would buy as much as 43 million tons of grain abroad in the current year.
The Western sources say the figure now appears likely to fall much closer to the 1980-81 figure of some 34 million tons.
The reasons for this remain unclear, but one explanation could be that the Soviets are having some success in reordering domestic agriculture and imports in favor of more protein-efficient types of feed grain.
Another explanation offered by Western business sources here is that Soviet ports, despite some recent improvements, just cannot handle more than 34 million tons a year, if that.
''This country has had three bad harvests and has done a lot of heavy importing as a result. . . . Workers get tired. Machines break down. The pace slows. This is inevitable,'' one businessman says.
Meanwhile, the Soviets have moved to diversify their sources of foreign grain since the Carter trade restrictions.
Officials here indicate the Kremlin still wants US grain. Its quality and quantity, and the efficiency of US export infrastructure, make it a good buy, the officials say. Moreover, if US farmers make money off the Soviet Union, they are more likely to favor good relations between the superpowers.
But the Soviets have also sealed grain ties with such states as Argentina, Australia, and Canada and thus reduced dependence on US supplies.
Of equal importance, the Soviets have been careful to purchase their US grain early in the US-Soviet grain year.
This helps free strained Soviet port capacity for shipments from other states , like Argentina, which harvest later. And at least this year, the early buying has amounted to a measure of insurance against new US grain sanctions.
The strategy requires help from Washington. And Washington - both in 1980 under Jimmy Carter, and this year under Ronald Reagan - has supplied it. The long-term US-Soviet grain accord that expires at the end of September 1982 provides for a spreading of Soviet purchases over the grain year. The idea was to prevent jolts to the grain market.
''But this year, for instance, we had a pretty good idea of how much grain the Soviets would need, . . . and we had a good harvest,'' a US source explains. So the provision was relaxed.
After talks in Moscow last September on the eve of the new grain trading year , a US official announced that the Soviets had been offered a total of 23 million tons of US grain, and that in his ''best judgment,'' they would take about 18 million of that amount.
The Soviets are now understood to have told US officials, however, that Moscow has no immediate plans to buy more than the 11 million tons already contracted. Some Western sources are suggesting the Soviets never planned to go above that amount and, in one source's words, ''have done some smart talking, and smart buying.'' Other sources caution that Moscow may still want to buy US grain later in the year, despite the present Soviet line.