It is 1987. A joint naval task force composed of American, British and French ships is sailing toward Saudi Arabia, where a new pro-Soviet regime recently has taken control. The Saudi king is in exile, and the United States supports his claim of sovereignty. When the task force is 500 miles from Saudi Arabia, the Soviet Union issues a stern warning: Stop or suffer the consequences.

The consequences? The Soviets will shut off 25 percent of Europe's natural gas supplies.

That may be fantasy, but by the end of this decade Europe actually could depend on the Soviets for that much of its natural gas. Natural gas, in turn, accounts for slightly less than one-fifth of Europe's total energy. Is this prospect a good or bad thing for the Western alliance?

That this question has received so little high-level attention reflects the alliance's tattered condition and outmoded foundations. Thirty-five years after World War II, our thinking about the Soviets -- and foreign policy problems in general -- remains excessively colored by military issues. If the past 15 years have taught us anything, it is the limited relevance of sheer military power (Vietnam) and the latent explosiveness of underlying economic changes (oil).

Nowhere is this clearer than in East-West relations, and yet the lesson seems to go unheeded. Even as Americans resurrect their old military obsessions, events emphasize the growing importance of non-defense matters. Consider:

Natural gas. European utilities are negotiating with the Soviet Union for a $10 billion to $15 billion gas pipeline to the West, probably delivering between 1 trillion and 1.5 trillion cubic feet annually. The Soviets already supply about 10 percent of Western Europe's roughly 8 trillion cubic feet of gas. Because Soviet gas reserves are nearly half the world total, European dependence could rise further.

Poland. The new Polish government has appealed to Western governments for massive loans to help it through its current economic and political crisis. Without new credits from somewhere -- The Soviets or private Western banks are the other political sources -- Poland may not be able to buy needed imports. Default on existing debts is a clear possibility.

Grain. After its second consecutive disastrous harvest, the Soviet Union is more dependent than ever on Western sources of food. Although the U.S. grain embargo probably didn't hurt the Soviets much in its first year, a continuation into 1981 might.

Trade. Exports from Western Europe and Japan to Communist countries comprise roughly 3 percent to 7 percent of their total exports. The United States falls in the same range, but U.S. exports consist mostly of grain, whereas other countries ship labor-intensive manufacturing products. In some countries, key industries such as steel and chemicals sell nearly 10 percent of their output to East Bloc countries.

Americans are uncomfortable with these developments. The Soviets are our adversaries. How can we trade with them? We like to think our foreign policy rests on a moral code. Yet, if the Europeans and Japanese trade when we don't, we think that we have been played for the sucker.

More than morality, we need to clarify our interests in this evolution. Basically, the rise of East-West trade reflects a world stretched increasingly thin for natural resources, technology and investment capital. The Soviet Union is no better off than the West and maybe worse.

Last year, its economy grew a mere 0.7 per cent, a shadow of the average 5.2 growth rate in the 1960s, according to the Central Intelligence Agency. Hampered by labor shortages, stagnating oil production and inadequate investment -- in part because both energy production and industry need scarce supplies -- the Soviets face hard times.

Trade clearly makes economic sense. For the Soviets, purchases of Western grain and technology help ease food and investment scarcities. For the West, Soviet oil and natural gas (which provide half the Soviets' hard currency to buy imports) relieve dependence on Middle East oil.

But does it make political sense? Depending on your reading of Soviet intentions, you can take one of two crude views.

Either: Stop it before it gets worse. Don't make things easier for the Soviets. Extend the embargo. Encourage the Europeans to find other energy supplies and avoid making themselves blackmail victims. Don't lend to Poland. Force the Soviets to bear the costs of their own empire, even if that means more political repression. An invasion would show the Soviets for the tyrants they are.

Or: Encourage it. Lend to Poland, because Poland is the best example of detente at work; that is, economic change is inducing political change. Buy Soviet fuel. The Soviets need the hard currency to buy Western oil exploration and development equipment. The more energy they find at home, the less likelihood that they will venture abroad.

Good points can be made on either side. The purpose here is not to settle the issue, but to argue that it needs to be confronted and not -- as it has been for the past decade -- sidestepped repeatedly. The American pursuit of detente has tried to have it both ways: to trade and cooperate, but to withdraw abruptly if the Soviets offend us. Such vacillation confuses both the U.S. public and our allies.

The trouble with this sort of "linkage" is that it generally doesn't work. Poor harvests may make the grain embargo a temporary exception. But, in most areas, the United States no longer has the technological leadership to exercise political leverage. The Soviets can (and do) go elsewhere. Attempting to make the Europeans and Japanese abide by our embargoes simply further strains our already strained alliances.

If the Western alliance is not as strong as it once was, it is because the United States no longer provides the economic umbrella that it once did. The growing trade between the East and West reflects, in part, the reality that the Europeans and Japanese no longer can rely on the United States as a residual oil supplier or as a growing export market.

Alliances are built on a sense of mutual interest. If we want more influence with the Europeans, we must give them a sense of security. This means refurbishing an economic alliance that has become rent with trade and energy conflicts. Among other things, it implies relaxing our claim on the world's energy supplies and leaving more for everyone else. This is a tall order. If we can't manage it, we'd better expect more East-West interdependence and prepare for the consequences.