PRESIDENT REAGAN has decided to extend grain sales to the Sovierong common ground was foundt Union for a year. He has a whole series of reasons why it's right and just for Americans to sell grain while it's deplorable for Europeans to sell technology and equipment for a Soviet natural gas pipeline to Western Europe. These reasons ostensibly relate to whether the transaction pulls hard currency out of the Soviet Union or eventually puts it in, whether or not the transaction contributes to Soviet military/industrial capability and so on.

The reasons are not entirely frivolous, but having studied them with some diligence we can report that they are most apt to be persuasive to people who are, at the moment of hearing, standing in a corn field. If you happen to be standing instead in, say, a compressor plant in West Germany, they are not likely to be persuasive at all.

It is no surprise that Mr. Reagan is keeping American farmers in the Soviet branch of the grain trade. He lifted the embargo his predecessor had imposed after the Soviet invasion of Afghanistan and gave not the slightest thought to reimposing it when the Polish crackdown followed last December. In respect to the grain trade, he accepts no real political linkage, although in making now a single- year grain agreement he pretends to be denying the Kremlin the comforts of a multi-year agreement: the farmer pressure to which he has bent all along ensures that grain exports will be perennial.

He does demand political linkage, however--to Poland--in the pipeline business in which the Europeans are engaged. That they object, on a host of political, economic and legal grounds, leaves him cold. All the toughness that one would expect him to direct at the Soviets or at the authorities in Poland is being brought to bear on this country's closest allies.

Our own view has been that sanctions entail a range of political conditions and economic links that do not lend themselves easily to sustained alliance-wide application. In principle, it looks attractive to deny the adversary something of value. But first of all it matters greatly who the target is--the huge disciplined Soviet society, for instance, or the relatively small and perhaps more vulnerable Polish regime? Then there is the question of paying the specific price. Who will pay? How? For how long? To what end?

These questions would be difficult enough if general economic conditions were excellent and the alliance was humming along smoothly on its other cylinders. In conditions of recession and disarray, they push the system to its limit. That is why we hope that the administration will figure out over the coming months how to assert its leadership in ways that ease the alliance back on a cooperative track.

A recent study suggested that the Soviet economy is substantially more dependent on foreign trade than had previously been believed. From this study, some people leaped to the conclusion that the Kremlin is indeed vulnerable to sanctions. That does not necessarily follow, given the alternatives and tradeoffs available to a totalitarian imperial power. The study is, nonetheless, suggestive.

It may be difficult under presently conceivable conditions to make the Soviet Union bend in specified ways to Western sanctions. But surely it cannot be politically irrelevant that Moscow has a large and continuing need for Western technology and capital. To leave this broad and vital commerce to the workings of the market seems a strange abdication of the collective responsibility.

That alliance agreement on an economic strategy may be slow and incomplete in coming is no reason to back away from the question. George Shultz would seem exactly the right man to frame the terms of such a common inquiry, as soon as the emotions now flaring over the pipeline can be subdued.