No one should be surprised at the popularity of President Carter's restrictions on grain and high-technology exports to the Soviet Union. Americans think they have taken a lot of abuse from foreigners in recent years, and they are enthusiastic about dishing some out in return. But we should not confuse popular policy with good policy. You do not stop tanks with grain, and the ruthless pursuit of economic sanctions against the Soviets is a policy with inherent limits and dangers.

At worst, it may undermine America's international political and economic power by straining relations with its allies, disrupting world grain markets and diverting attention from the more fundamental military nature of the Soviet threat. Unless carefully understood, a policy intended to make us stronger may have the opposite effect.

For years, we have had simplistic ideas about the roles of economic and military power. We believed that increasing trade with the Soviet Union constituted a subtle form of disarmament. Greater interdependence would lead both sides to reduce relative military spending. We did, but they didn't. Consequently, the Soviets devote about twice as much of their national output to defense (11 to 13 per cent) as the United States.

If we now believe that trade restrictions will significantly weaken the Soviets, we risk making the same mistake in reverse. With a little bit of luck -- good for us, bad for them -- we can cause conspicuous inconvenience, but not much more. Even in grain, the Soviets depend on import for only 5 to 15 per cent of their consumption. In high-technology areas, machinery imports constitute only a small proportion (1 to 3 per cent) of annual Soviet investment that exceeds $300 billion. And the United States ranked only fifth as a supplier of high-technology goods in 1977, according to a recent Commerce Department study.

It's true that the Soviets face enormous economic problems in the 1980s. Oil production may soon peak, if it hasn't already, and there will be staggering strains in Soviet labor markets.

But none of this means that any economic hurt we inflict on the Soviets advances our interests. In the evolving struggle for Middle East oil, those interests are simple: to keep the oil flowing; to keep Soviets out; to make the Persian Gulf nations more receptive to American than Soviet protection; and, if worse comes to worst, to assure that our traditional alliances with Europe and Japan remain as cohesive as possible.

Indiscriminate economic warfare against the Soviets does not necessarily serve these interests. The one high-techology area where we might hurt the Soviets most is the one in which -- in our own interests, not theirs -- we ought to want to hurt them the least: oil exploration and production equipment. The more Soviet oil production declines, the more attractive Mideast oil supplies become and, incidentially, the more pressure builds for further price increases, which weaken Western alliances.

The damage the United States can do to Soviet food supplies is more immediate, but probably not sustainable. Even if the Soviets can't quickly make up all the lost U.S. grain sales, no respectable food analyst believes the impact on meat supplies (most grain is used as animal feed) will exceed the effect of the disastrous 1975-76 Soviet grain harvest, the worst in years. The Soviets then slaughtered large numbers of hogs and poultry, and, after feeding these animals to the public, imposed meatless Thursdays. In 1976, per capita meat consumption dropped 10 percent.

But keeping the Soviets permanently away from world grain supplies will be difficult. Although the United States is the largest exporter (accounting for 50 to 60 percent of the world total), there are numerous others, and shipments through third countries are not uncommon. Any long-term effort to block sales to the Soviets would probably result in a shuffle of customers and suppliers; the Soviets would pay slight premiums for grain, separating traditional suppliers and buyers. The latter would come to the United States. Already, the Soviets are believed to have offset some loss of U.S. grain with purchases from Argentina.

The simplest way to frustrate this process would be to hold large amounts of grain off the world market, but the cost to the United States would be great. Grain prices would rise, causing inevitable and understandable outrage among our principal allies, Europe and Japan, who are also our biggest customers. Keeping U.S. farmers happy would cost the Treasury additional billions of dollars for high price supports, acreage set-aside or other subsidies: billions that would probably be better spent producing guns rather than not producing grain.

Limiting exports to the Soviet Union may satisfy a gut instinct against trading with your "enemy," but we shouldn't regard -- as we have -- such trade restrictions as a substitute for military spending. By the combination of a strong military and liberal trade policies, we ought to be encouraging the Soviets to use trade, not force, to solve their problems at home.

Looming manpower shifts, for example, will increase Soviet need for the productivity inherent in Western industrial technology. For most of the postwar period, Soviet economic growth depended heavily on putting more people to work: 2.3 million on average during the 1970s. In the 1980s, the increase will average only 550,000, according to Census Bureau demographer Murray Feshbach. More disturbing to the Soviets, the entire increase will occur among the low-skilled Moslem population of Central Asia.

With these new problems added to the old -- a large defense sector that siphons away the best managerial and technical talent, confusing "incentives" for factories and inefficient farming -- you can understand why the commissars worry about the 1980s. Soviet meat consumption is still half America's, and at least one-fourth of urban families share living quarters.

Peace is in our interest, too, and if the Soviets find that their economic and political frustrations are best relieved by adventurism abroad, that supreme interest will suffer. If we had -- which we do not -- the capacity to project a credible military presence in the Persian Gulf, we would not be so worried about Afghanistan. In current circumstances, curtailing exports to the Soviet Union may have been the "signal" we could send. If their 1980 harvest is poor, it may pinch. But it is a stopgap, not a policy, and it may boomerang.