It does not cheer anyone but the Russians that the Western alliance is in such turmoil. Indeed the front-page news that the European Economic Community has officially protested the American ban on sales of pipeline equipment to the Soviet Union as ''unacceptable interference'' evokes sadness. Allies are not expected to march in step at every twist and turn, but when a falling out reaches the point of formal protest notes it concerns all who value allied cooperation as a strong bulwark against Sovietism. President Reagan will want to find a way out of the uncomfortable position in which the United States now finds itself.As he takes up the EC protest, a number of questions need to be addressed:
* Will the US sanctions delay the natural gas pipeline as hoped? The Europeans assert it is ''unlikely'' construction will be materially delayed. So the US, if it persists in its ban, would be making a cause celebre of something that is bound to occur anyway.
* Is the ban legal? The administration claims that it is, but the EC says it violates international law and possibly some ''rules and principles'' of US law. Only international lawyers can argue out this complex subject but, even if the US decides it has a solid legal case, it will have to ask whether pursuing the ban is worth the political cost.
* What will the US sanctions do to the credibility of American business? One worrisome fallout of the ban is that West European firms are questioning the reliability of deals with US firms when political considerations are permitted to intrude so strongly.
* Will Siberian gas create a dangerous West European dependency on the Soviet Union? The issue is not minor. But the EC argues that, even when flowing at the maximum rate in 1990, it will account for less than 4 percent of the EC's total consumption of energy from all sources.
* Will the US ban appreciably hurt the Soviet economy? The West Europeans contend it will only spur the Soviets to accelerate development of their own technlogy, a view for which there is an historical precedent. In the mid-'60s, when the US successfully blocked West German sales of wide-diameter pipe to the Soviet Union following the Cuban missile crisis, the Russians proceeded to develop their own -- and even larger -- pipe.
* Most important of all, will the pipeline sanctions really affect the situation in Poland? This is Mr. Reagan's principal argument, yet it is a weak one. It is naive to think that the Soviet leadership will let Western economic arm-twisting dictate its policy in Poland, where it has overriding strategic and political interests. Martial law will be lifted only when the Polish military leaders and their Soviet patrons feel the communist system is no longer threatened.There can be no benefit in a US-European showdown. If the administration persists in its course, it may find future American exhortations being ignored when they concern matters of far more strategic importance. It will not be easy politically for Mr. Reagan to reverse course and cancel the pipeline ban, but the fact that the Polish authorities have eased some martial law restrictions provides him an out.For the sake of allied harmony, the US must end the pipeline confrontation -- and then proceed with its partners to work out new and stronger guidelines for East-West trade. The pipeline controversy is not the cause of disunity in the alliance but only a symptom of it. The need is to get quickly to the larger question of the rules by which the West conducts business with the Soviet Union.