Regardless of the ultimate outcome in Poland, one important new development is clear: The long-established Brezhnev Doctrine is in decline.

It may persist as a Soviet unilateral declaration, but its days of multilateral acceptance, or tolerance, are waning. By their surprisingly strong reaction to the Polish crisis, the United States and its allies have said, in effect, that they are no longer willing to acquiesce in Russia's assertion of hegemony over the Soviet orbit, especially Eastern and Central Europe.

That is a momentous change that could lead to a more benign world or, if pushed to East-West confrontation, could trigger the worst of all worlds -- nuclear conflict. It all depends.

On the basis of President Brehnev's utterances at the Prague meeting last week, there is reason to believe that he now realizes his doctrine of hands-off the Soviet sphere of influence is no longer exempt from challenge.

Whether the Kremlim can finally reconcile itself to this new Western stance remains to be seen. After all, Russia cracked down on East Germany (1953), Hungary (1956) and Czechoslovakia (1968) with little more than pro forma protests by the Western powers.

Although the United States and its allies never explicitly acknowledged the validity of the Brezhnev Doctrine, they in practice respected it for a good many years. So it is hardly surprising that Moscow still seems uncertain what to make of the vehement reaction over Poland. Why Poland all of a sudden?

Well, it isn't just Poland. Times have changed since 1968 and the Cechoslovakian revolt. Russia is no longer the ever-expanding force it seemed to be 13 years ago when it was the acknowledged leader of the entire communist world.

Now, instead of dominating a billion Chinese, the Soviets have to keep 44 divisions on a hostile China border. The Russian's strategic foothold in the Middle East was lost when they were ejected by Egypt and Sudan. Indonesia is gone; likewise many of Russia's former clients in Northern and Western Africa.

Virtually all the communist parties in free europe have asserted their independence. In the event of war, Moscow has to face the prospect of its Warsaw Pact satellites' fighting against it rather than for it. Meanwhile, Soviet resources are being severely drained in Cuba, Afghanistan and Ethiopia. The upshot is that a Polish crackdown will mean virtually global isolation, possibly leading to what Moscow fears most -- encirclement by an entente of the United States, NATO, Japan and potentially colossal China.

On the other hand, what happens if Poland gets away with this resistance? The communist Czechoslovakian leader, Gustav Husak, speaking in the presence of Brezhnev a few days ago, had good personal reason to reaffirm the Brezhnev Doctrine in the strongest terms, for if the Polish revolt becomes contagious, Husak could be the next casualty.

People in the Warsaw Pact nations are certain to conclude that they, too, can expect help and protection if the United States and its partners are prepared to go to such great lengths for an independent Poland. Hence if Russia fails to stamp out Polish dissidents, it can only look forward to more of the same elsewhere.

It is an excruciating dilemma for the Kremlin, perhaps the most acute it has faced in the post-war era. In making its final Polish decision, Russia has to choose between preserving its empire at any cost, or electing to pursue a less-ambitious policy of joining the world, promoting detente and disarmament and gradually relaxing Soviet hegemony.

Brezhnev's speech in Prague was notably less harsh than Husak's, and his conciliatory remarks coincided with the termination of Soviet troop maneuvers in the Polish region. Although there is still no guarantee that Russia won't intervene later on, it would seem advisable for the West to let Moscow back off with as little loss of face as possible.

At this point, there appears to be not much more to be gained by continuing the tough warnings and threats of retaliation that have been issuing almost daily from Washington. We have obviously made our point; further ultimatums could be counterproductive.

Despite the skepticism of the Reagan administration, our NATO partners still believe it is possible to negotiate a stabilizing detente with Russia. They are eager to get on with the limitation of strategic weapons and the mutual reduction of forces in Europe, and they don't want a belligerent Washington to dash these hopes.