In a strange twist of international diplomacy, the U.S. partial embargo of grain sales to the Soviet Union has made this Soviet Bloc country increasingly dependent on American feed grains.

In the year after Jimmy Carter's cutback in grain shipments to the Soviet Union East Germany's imports of U.S. corn doubled. U.S. agricultural officials believe this shift was coordinated by Moscow to free gain from non-American sources for sale to the Soviet Union.

These shifts by East European customers such as East Germany and Czechoslovaki helped cushion the blow that the embargo could otherwise have dealt the Soviets.

But while these altered grain trade patterns indicate the difficulties of making such embargoes effective, the 15 months of the embargo also have driven home to East German agricultural planners how vulnerable they are to politically motivated curtailments of their grain supplies.

As East Germany has moved away from small-scale family farming, it has required increasing volumes of imported feed grains and soybeans to supply the calories and protein for its intensive meat-producing operations. This, in turn, has tied the country into an international grain market dominated by the United States and subject to U.S. political pressures.

This is not a situation that communist planners are happy about. In a recent speech, East German Premier Wille Stoph noted the "strategic" importance of grain for the first time and called on the country's system of centrally planned, government-operated agricultural cooperatives to grow more of their own feed in the next five years.

But American experts doubt that this dependency can be reduced significantly. The East German communist government has implicityly acknowledged a long-term commitment to substantial grain imports with its construction of a multimillion-dollar grain terminal at its main Baltic Sea port of Rostock. The facility, using foreign technology and paid for with foreign currency, will be capable of rapidly unloading ships. It has the strategic advantage of making East Germany less dependent on the West German port of Hamburg.

There are also rumors that the East German grain-trading enterprise Nahrung may establish an office in the United States to coordinate its deals for American commodities with multinational grain companies, which handle the bulk of grain exports from such key ports as New Orleans, Houston, Duluth and Norfolk.

In 1980, the first year of the embargo, East Germany imported about 3.3 million tons of feed -- about one-fourth of its total requirements. Nearly 3 million tons of that was corn or soybean meal orginating in the United States. The bill for the commodities was around half a billion dollars.

That the East German livestock industry is locked into a prolonged dependence on these imports is evident from a visit to the headquarters of the 11,000-acre agriculural cooperative here that specializes is hogs and cattle.

Cooperatives such as this one have helped make East Germans the bestfed people in the Soviet Bloc and have positioned East Germany as the most efficient agricultural producer in the region

East Germans this year will eat an average of 210 to 220 pounds of meat, a third more than a decade ago and as much as some Western countries. But the efficiencies that have made these advances possible depend heavily on acess to high-grade imported feed.

This is one reason why many agricultural experts are skeptical of claims that the American embargo had negligible impact on the Soviet Union.

Last year, the Neuholland co-op produced 1,200 tons of beef and pork with 4,000 tons of feedstuffs, and last month it took about 4.4 pounds of feed to add one pound of gain to the co-op's hogs, according to director Peter Nietz. U.S. experts consider these ratios respectable and appreciably better than in the Soviet Union. U.S. ratios run around 2.4 to 1.

Nietz gets about 2,500 tons of feed each year from the cooperative's own farmlands, mainly in potatoes, silage, alfalfa and some grain. But he depends on another 1,500 tons from the state grain company. The bulk of this appears to be imported U.S. corn or soybean meal.

"We think we can increase the amount of feed we grow ourselves," said Nietz. "The question is how much.

So far the substitution of locally grown grains for imports has been slow -- around 100 tons a year. As Nietz points out, this countryside north of Berlin once was nicknamed "God's sandbox," because of the poor soil, which is an obstacle to improving grain production.

More is at stake in maintaining the success of farms such as this than just economics. Politics is also involved. Inevitably, agriculture has been drawn into the bitter ideological debate between Poland and its block allies.

Poland's private farmers, who still produce the bulk of that country's food, have gained unprecedented official recognition of their Rural Solidarity union. But officials here note that an agricultural worker in East Germany feeds 18 persons, compared with only seven in Poland. While food shortages are worsening in Poland, East Germans this year will eat more meat that at any time since World War II.

Therefore, the message preached here is that the socialist model of huge centrally planned farms -- backed by infusions of capital and technology -- works. By the same argument, years of appeasement of Poland's private farmers by the Communist Party in that country is said to have led to economic disaster.

In the 1950s, the Soviet-backed East German government ordered the forced takeover of farming by state-operated cooperatives. It was a bitter period that forced the emigration of thousands of farmers and led to the stagnation of East German agriculture for years. Now, officials say, they are finally harvesting rewards from that painful period.

"The capitalist countries achieved their efficiencies through a process of small farmers being swallowed up by larger ones," said Nietz. "We did it by forming socialist cooperatives. Frankly, we consider our way more humane, but we understand that's a matter of debate. But Poland has done neither. It has the worst of both systems and the benefits of neither."

U.S. experts credit East Germany with developing "big-time agriculture on the right scale." And they refer to heavy investments in the last 10 years in fertilizers and bigger tractors. About 20 percent of the livestock now are raised in modern, disease-free facilities.

Several years ago, East Germany invested $100 million in an automated slaughtering plant that turns out 120,000 tons of sausage and ham a year with the help of American-built computers.

Some of the costs of the imported grain and technology are offset with sales of beef and pork to West Germany, but the agricultural trade deficit still is substantial and suggests the importance that the government attaches to food.

The payoff, say officials, is efficiency. Only about 10 percent of the country's food supply now comes off private plots, compared with 30 percent in the Soviet Union, and East Germans eat about 60 pounds more meat a year than the Soviets do.

Still, U.S. experts put forward another statistic to offset enthusiasm for East Germany's farming accomplishments; West Germany's family farmers feed on average of 34 persons each, about double the figure in East Germany.