Don't look now, but that Soviet client nagging Moscow to resume detente is none other than rigid, hard-line, orthodox East Germany. The Feb. 21 all-day visit to East Berlin by Assistant Secretary of State Richard Burt is recognition of this curious fact. Mr. Burt is the highest-ranking American foreign-policy official ever to visit East Berlin.
It is also tacit American recognition that the West Germans were right to preserve as much detente as possible in Central Europe even during the revived cold war that followed the Soviet invasion of Afghanistan.
As an informed source describes it, Burt was to sound out ''the possibility of continuing East-West dialogue.'' In particular, the aim was to undercut Soviet claims that the new NATO Euromissile deployments have created a crisis situation and to press US proposals for arms control by taking advantage of East European misgivings about new Soviet missiles in East Europe.
East Berlin's new role in promoting detente is so contrary to the conventional wisdom of the past quarter century that some explanation of the background, evidence, motivation, and trade-offs of the East German shift is necessary.
Roughly ever since Stalin's death in 1953 the practice has been that the more an Eastern European country strained at the Soviet leash, the more eager it was for better East-West relations. Detente created a less tense atmosphere in which Romania could get away with defying Soviet foreign policy - or Hungary could experiment with market-type economic reform.
The hard-line East Germans were the conspicuous holdouts to such trends. Once the Soviets themselves opted for detente, in fact, Soviet leader Leonid Brezhnev had to dump East German leader Walter Ulbricht. Ulbricht's replacement, Erich Honecker, went along with the German-German version of detente, called ''Ostpolitik'' in Bonn.
But he was wary lest the resultant liberalizing of East European societies get out of hand and destabilize their governments. In 1980/81 Honecker criticized the rise of Solidarity in Poland more sharply than did any other East European leader (except Czechoslovakia's Gustav Husak).
During the freeze in East-West relations after the Soviet invasion of Afghanistan, East Berlin did seek to maintain the special German-German relationship. Many Americans interpreted this as a bald attempt to woo West Germany away from the American alliance, however, rather than any East German devotion to overall East-West detente.
When West German Chancellor Helmut Schmidt alluded to East German restraint on the Soviet Union (as well as West German restraint on the US) during his ill-timed summit with Honecker on the weekend martial law was imposed in Poland in 1981, this was treated as a bad joke in Washington.
East Germany's willingness to contradict the Soviet line became apparent as NATO began deploying its new missiles at the end of 1983. The Soviets walked out of the Euromissile arms control talks in Geneva, saying they would not return until NATO removed its new missiles.
And Moscow did its best to stimulate a mood of East-West crisis, both verbally and in new ''counterdeployments'' of short-range nuclear missiles in Czechoslovakia and East Germany.
Initially Honecker echoed the Soviet forecast that NATO deployments would usher in a new ''ice age'' in inter-German relations. But even before the Pershing IIs and cruises touched European soil, he was stressing the need for ''limiting the damage'' in East-West relations.
And he increased by 40 percent the number of working-age East Germans allowed to go West for ''urgent family reunification'' in 1983.
The two German states, Honecker and West German Chancellor Helmut Kohl agreed , were joined in an ''association of responsibility'' to help prevent war (and, by implication, tensions that could lead to war).
Even as Moscow was declaring it would not resume nuclear arms control talks until the NATO missiles were withdrawn, Honecker asserted the Soviets would eventually return to the negotiating table.
Even more remarkably, Honecker expressed public misgivings about the new Soviet missiles in East Europe. And there already were more missiles (in Eastern Europe) than the West realized, he added - leaving some listeners to infer that no more were needed.
East German Defense Minister Karl-Heinz Hoffmann and Bulgarian President Todor Zhivkov have also publicly drawn attention to the financial burden the East Europeans have to assume in paying for the Soviet missiles.
And in an unprecedented move well before the NATO deployments, the East German party newspaper Neues Deutschland printed a letter from Lutheran pastors expressing horror at the new Soviet as well as the new NATO missiles. More discreetly, hard-line Czechoslovakia aired reservations about the new Soviet missiles.
These developments occurred in the last months of Soviet President Yuri Andropov's life. The West saw them primarily as East European maneuvering for more elbow room in a time of leadership uncertainty in the Kremlin.
But Honecker's lobbying for relaxation of East-West tensions continued even after the new Soviet party general secretary, Konstantin Chernenko, took office.
Immediately after the announcement on Feb. 10 of Andropov's death, Honecker told an East Berlin party conference that everything must be done ''to use every possibility to let common sense and realism prevail, to replace confrontation with cooperation, to make progress in disarmament, and to revive detente in accord with the principle of equality and equal security.''
When Honecker and Kohl held their first summit - in Moscow on the eve of Mr. Andropov's funeral - Honecker came with a prepared statement for the two leaders to issue after their talk. It emphasized their mutual interest in further East-West dialogue. It spoke of the ''existential importance'' of avoiding nuclear war and of using ''common sense'' to search for ''practical solutions'' to prevent ''the course of international affairs from getting out of control.''
As examples of this search it praised the Stockholm conference on confidence-building measures in Europe and the conventional forces reduction talks that will resume in Vienna in another month.
The statement did not mention the suspended nuclear arms control talks, but the West Germans came away from the meeting convinced Honecker wants these talks , too, to be resumed - and thinks there is a real possibility Chernenko will resume them.
Honecker's motivation in all this seems to be largely economic. Even more than most other East European countries, the East German government depends on raising the living standard of its citizens for its legitimation (since any nationalist alternative would risk enhancing the attraction West Germany holds for the East German man in the street).
East Germans already live better than any other East Europeans. The East German economy had the second-highest growth in the Soviet bloc last year.
But there are growing bottlenecks, including fuel shortfalls. And after a decade of subsidizing East European energy, the Soviet Union has too many economic problems of its own to continue bailing out its clients.
So West Germany is East Germany's only economic savior. And the understood condition for gestures like Bonn's 1 billion mark ($370 million) credits to East Berlin last year is relaxation in East-West German relations.
But in the long run, Moscow can permit relaxed East-West German relations only within a broader relaxation of overall East-West relations. Hence the East German interest in a return to something approaching detente.
Soviet tolerance of this East German lobbying seems to derive from the special importance to Moscow of East Berlin, and from a balancing of risks.
Thus, East Germany is an ideological stalwart in the Soviet bloc, backing and even urging Soviet disciplining of liberal heresies, aiding Soviet promotion of revolution abroad by sending a few thousand East German military and police advisers to ripe third-world countries. East German industry also supplies much of the modern technology needed by the Soviet Union. And East Germany is the greatest prize in Moscow's postwar buffer zone in East Europe - one the Soviets deem worth securing with 19 of their 30 divisions in Eastern Europe.
If Honecker says he needs a robust economy to ensure political stabilization then - and if the Soviets can't provide the necessary economic help - Moscow is inclined to let East Berlin go ahead and get help from Bonn, even if it must accept the price of inter-German detente.
For the Soviets the risks of Eastern European contamination in such a course are not too high, since the East German leadership itself is so orthodox.
Since detente began, the East German leadership has shown remarkable skill in allowing its citizens unlimited access to alien West German radio and television and in welcoming 6 million West German visitors a year - all without destabilizing party rule or ideological control.
For a few years the West Germans have been watching this evolution of East German policy. The slow, stable opening of a country like East Germany to Western contacts has always seemed much more durable to them than the headlong rush of a Poland in spurts that alarm the hegemonial Soviet Union and set off a backlash.
The latter-day American appreciation of East Germany's position, by contrast, reflects an altogether new sophistication in Washington. In the past, high US officials would visit Romania or Hungary or Poland (during liberal phases), but never hard-line East Germany. Usually the aim was to dramatize how far the country being visited was diverging from Soviet practices.
This week, however, Richard Burt is visiting the model conformist states of East Germany and Bulgaria in addition to economically experimenting Hungary.
At this point the US sees an advantage in dealing with the orthodox states of East Europe - and in reinforcing their novel moderating influence on Moscow.
WHERE MISSILES GO IN EAST AND WEST GERMANY
Missile Location Range WEST GERMANY 108 Pershing IIsMutlangen (9 already deployed) 1,085 miles Neu Ulm (no deployments yet) Heilbronn (no deployments yet) 96 cruises Undisclosed 1,550-1,860 miles EAST GERMANY SS-22 One reported sighted 335-620 miles in Bernsdorf SS-21 Undisclosed 40-75 miles The NATO missiles are being deployed to counter the approximately 260 triple-warhead SS-20s in the Soviet Union aimed at Western Europe. The SS-20 has a range of about 3,410 miles.