That was a remarkable report on Soviet agriculture that was presented recently in the Kremlin. No doubt the submitting of it, not to speak of the leaking of it to The Post's Moscow correspondent Dusko Doder, had something to do with the politicking over the succession to the aging Leonid Brezhnev. Somebody in the Soviet leadership must think there is political advantage in showing what a hash Mr. Brezhnev has made of agriculture in his 18 years of power.

And a hash it is. For decades the Soviets have been pleading bad weather in extenuation of their farm failings, whose effects are seen in the shabby diet forced upon all but a favored few Soviet citizens and in huge and now seemingly permanent food imports ($7.2 billion worth in 1980). The new report, however, cites a broad range of man-made failings and concludes that the "existing economic mechanism does not provide necessary economic incentives for production increases and fuller use of the potentially available land." One wonders just what was intended by the phrase "existing economic mechanism." Some critics of the existing agricultural order, and not only the agricultural order, might take it as a reference to the socialist system as a whole.

In any event, it was a heck of a report. It was apparently too strong for the ruling Central Committee, which simply approved another batch of the timid half-measures whose inadequacy has been confirmed almost annually through the Brezhnev years. If there is to be a fresh and effective approach, it awaits a turn of the political wheel.

Meanwhile, there is an American interest, which has been compromised for far too long. Over the last 20 years, American food exports have made the United States the final guarantor of the Soviet diet or, to put it another way, the savior of the Soviet agricultural system from itself. The dependency has left both great powers ambivalent, with Moscow fretting about the hazards and indignity of dependence while Americans wonder whether the profits compensate for the great political relief that the Kremlin reaps from the exchange.

Secretary of State Haig, commenting on the Soviet farm report, declared the other day that Soviet failures provide the United States with an opening for political leverage. "We must force our principal adversary, the Soviet Union, to bear the brunt of its economic shortcomings," adds a new White House policy directive meant in part as a rationale for insisting that the European allies stop furnishing technology and credit so freely to the Soviet bloc. Even as one set of officials speaks, however, another set is negotiating a new, long-term grain agreement with the Soviet Union and approving a new wrinkle in the grain trade: the financing of grain purchases by a cash-short Soviet government by means of short-term commercial loans.

Mr. Reagan's reasons and arguments for continuing to sell grain to Russia are no more acceptable for being familiar and well known. The grain trade cuts completely across the whole stated thrust of his foreign policy and makes him look silly when he asks other nations to hold back on a gas pipeline, on high technology, on credits and so on. Many people who have reservations about some aspects of current foreign policy are offended by the notion of a Soviet adversary's buying its way out of trouble courtesy of Ronald Reagan and bidding up the price of food in the American and world markets.

If Mr. Reagan is not prepared to restrict these exports--in a way that ensures that American farmers alone will not pay the cost--he should say so and accept the foreign policy consequences, however embarrassing for him these may be. It can hardly be more embarrassing than the role he is now playing as the man of the year in Soviet agriculture--every year.