In 20 pages of texts and graphs in their last issue of 1981, the editors of The Economist set forth their view of the East-West struggle, as it developed in the two years from the Soviet Union's invasion of Afghanistan to the imposition of martial law in Poland.

The British journalists suggest at the outset that they tailored the article for the attention span of a reader named Reagan, who, they said, "rises lateish, except when they wake him up with news of tanks in Poland, or whatever; takes an early-afternoon break; devotes most of his time to American affairs; and leaves the Oval Office early." Except for this gratuitous dig at our peerless president, it is a first-rate piece of work, but not a cheery introduction to the new year.

In calm terms, The Economist argues the case that "the road from Afghanistan to Poland has changed the way in which most Americans --and many, though not yet enough, West Europeans--look upon what Russia is trying to do in the world.

"Until 1979, the prevailing view was that Soviet motives were primarily defensive. Russia's buildup on its frontiers with Western Europe and China seemed only natural to a country faced by a threat on two flanks," the writers say, even though the buildup extended to nuclear weapons and consumed an "astonishing" 11-to-14 percent share of the total Soviet output.

But since 1979, "this comfortable view has had to be reassessed," The Economist says, because "the Soviet government has increasingly seemed to be presiding over a frightened and therefore dangerous system of imperial power. As the challenges to the system build up, Russia's great and growing military strength is deployed both to extend the system's frontiers and to save it from internal disintegration."

The writers make the point--as Ronald Reagan did in some of his early presidential comments--that an empire in decline can still be a very dangerous force in the world. Indeed, the Soviet Union's inability to compete effectively in the economic or political realm does appear to be increasing its dependence on the force of arms.

That requires what the United States is now doing--a program of countervailing rearmament, designed to deter the Soviets from taking even greater risks in the military arena. But it also requires that the United States and its allies take the steps necessary to preserve their present advantages in the economic and political realms.

This means, first, that despite the difficulties many of these nations are facing in their internal economies, they must resist any greater tendency to buy their own prosperity at the expense of their allies, through restrictive trade policies.

It means that the European allies must temper their appetite for trade with the Soviet bloc by a realistic awareness that trade can be an effective weapon against Soviet military expansionism. But it also means that the United States must temper its special interest in Taiwan by a realistic awareness of the vital importance of keeping China and the Soviet Union apart.

In the Middle East, there is need for accommodation by the Europeans and Americans--to say nothing of the Arabs and Israelis. But the critical arena remains Europe itself.

The worst thing that has happened in Poland is the repression of a movement that could have reshaped the future of that nation and raised the hopes of other peoples subjugated for a full generation by Soviet military power. But the second worst thing that has happened is the dramatization of Western Europe's seeming inability to react and respond to the tragedy and threat on its own doorstep.

As The Economist editors rightly put it: "The United States has reason to worry about the constancy of its European allies. But the bigger immediate danger perhaps lies within America itself. . . . Public opinion in the United States may before long weary of Europeans who chant anti-American slogans, and shrug about Poland, while relying on American protection-- and, cheekier still, relying on America to make sure they can get their oil from the Gulf."

Poland has shown the economic and political failure of the Soviet empire and its increasing reliance on military repression. But it has also shown the wavering of the West--and that is also very bad news.