Western diplomats are puzzled by and wary about Soviet fiddling with Western flight altitudes in the three air corridors from West Germany to West Berlin. No clear pattern of pressure has emerged in the stream of Soviet requests for changed Western flight altitudes over the past two months. But the unusual frequency of the requests spurred the United States, Britain, and France to protest formally to Moscow in early March against unilateral claiming of space in the air corridors for temporary Soviet use.
The Soviet reply was ''generally unsatisfactory,'' according to a Western diplomatic source and did not resolve the issue - but on the other hand did not lead to any ''crisis.'' The diplomat noted that all three allies are ''keen on preserving our rights to fly there in an unrestricted way.''
Since the protest the Soviet requests have continued for Western flight alterations to avoid possible collision with Soviet MIG fighters participating in exercises in western East Germany. And a ''sighting'' of a Soviet fighter that twice flew within a mile of a Pan American airliner on April 5 further dramatized the situation. That incident was similar to an earlier one Feb. 16 in which a British Airways liner was shadowed by Soviet aircraft.
The West is publicly playing down the incidents, while privately making it clear to Moscow that they are a cause for concern. Under postwar agreements, the US, Britain, and France as the occupiers and protectors of West Berlin are guaranteed free use of three air corridors across East Germany to West Berlin - a right that has been especially sensitive ever since the Soviet road blockade and the Western airlift to Berlin in 1948/9.
According to a Western diplomat who monitors the situation, no Western civilian or military flight to or from Berlin has so far been canceled, postponed, or endangered by Soviet requests for altitude changes. Nor have daily Western helicopter flights along the Berlin wall and out to West Berlin's own little enclave of Steinstucke in the southwest of the city been affected in any way.
It is assumed that the Soviet requests will taper off as the current Soviet military exercise comes to an end - in mid-April, if the usual schedule is followed.
One curious sidelight of the Soviet requests is that Western planes have several times been asked to fly above 10,000 feet (and have complied) - an altitude that the Soviets normally set as the ceiling for Western planes. The three Western powers do not accept any Soviet right to impose a ceiling or restrict flights in the corridors in any way. The 130 daily flights usually stay between 5,000 and 10,000 feet.
The Soviet requests for changes in Western flights are made in one of the only two four-power organizations still functioning from the time of the early postwar allied occupation of Berlin: the Berlin Air Safety Center. This center routinely coordinates flights and approves alternative altitudes or reroutes planes. Given European weather conditions the center is quite active, since, as the diplomat pointed out, it is ''not a smooth, simple operation like running the Phoenix airport.''