Just over a month ago, when Soviet President Leonid Brezhnev was here, West German Chancellor Helmut Schmidt described his own role in the East-West talks as that of an "interpreter" between the superpowers.

It was an artful construction that allowed the West German leader to pursue his country's preoccupation with arms control and detente while at least appearing to be performing a valuable service for the United States.

Schmidt's formulation nonetheless highlighted a cardinal rule of Bonn's diplomacy: always wrap German positions in a Western mantle because political isolation is too discomfiting for a Germany that remains highly dependent on Western military strength and ever eager to be seen as loyal to the community of democratic nations.

But the crackdown in Poland has presented Schmidt with perhaps the most stressful integration of West German policy with U.S. aims since the launching more than a decade ago of Bonn's Ostpolitik, or Eastern policy.

Schmidt has been speaking a different language on the imposition of martial law in Poland than the tough remarks and actions advanced by President Reagan. When he visits the White House Tuesday, Schmidt will be forced by events to interpret his country's cautious, reserved reaction.

Bonn's chief argument so far for avoiding sanctions is that such measures could upset chances for the resumption of talks between Poland's Communist Party, the suspended independent trade union Solidarity and the powerful Polish Catholic Church.

In the West German view, the threat of punishment by the West, rather than the act itself, is the best inducement for the Communists to return to a moderate course in Poland. West German officials argue that to enact sanctions now--particularly economic sanctions which are rarely effective anyway--the West loses whatever leverage it had to keep the Soviets from marching into Poland and finishing the disciplinary job that Poland's leader, Gen. Wojciech Jaruzelski, began three weeks ago.

West German officials remain inclined to give the benefit of the doubt to Jaruzelski's declared intention to reinstate some degree of reform once order is restored.

Underlying this assessment is Bonn's commitment to cooperating with the Soviet Union and its East European allies, a commitment seen here as the only way to maintain stability in Europe. West Germany's approach toward the Polish crisis draws from the same impulses--for sustained trade, for East-West German family contacts, for peace--that drove the development of Bonn's Eastern policy.

At the root of the West German position is a conviction--which comes across clearly in talks with German officials--about the best way to reason with leaders of the Communist Bloc. This understanding, which favors dialogue over confrontation, is born, one ranking German official said, of living next door to Eastern Europe and doing more political and economic business with the Communists than any other Western nation.

West Germany is still in a recession and would find a drop in its trade with the East particularly damaging. Among the major new job producers to come along in recent weeks was the signing of the West German financing and gas contracts for the major gas pipeline that will supply at least six Western European countries with Siberian natural gas into the next century. Reagan has suspended the export licenses for those U.S. companies involved in the pipeline project.

If Bonn's outlook is biased by its investment in detente, West German officials worry that the Reagan administration's approach to Poland may be tilted to a potentially dangerous extreme by its attitude toward cooperating with the Soviets.

The current balance of power in Europe grew out of the last war, a point Schmidt recalled in a newspaper interview published yesterday that sounded like a warning to Washington. He said the West had agreed at Yalta in 1945 to divide Europe into spheres of influence, and any attempts to alter the balance of power in Eastern Europe would mean war.

The remark was odd in one sense: West Germany is constitutionally committed to try to alter the balance by reuniting with East Germany. The remark was also revealing of the current mood in West Germany--unease laced with fear that the situation in Poland could explode into a larger East-West conflict.

French President Francois Mitterrand also mentioned Yalta in his New Year's address, but the way the French Socialist leader brought it up points up the difference in outlook between West Germany and its closest Western European ally. Mitterrand said everything that permits the West to supersede the Yalta agreement is positive, although he added that the wish to do so should not be confused with today's reality. It was a conditional remark, coming to the same point as Schmidt's, but conveying a clearer moral judgment.

Mitterrand may prove to be as reluctant as Schmidt to endorse sanctions against the Polish Communist Party and the Soviets, but the Frenchman's rhetoric, together with statements by leading Italian and British officials, sounded more severe than the West German's in condemning the stifling of Polish rights and acknowledging a Soviet role in Warsaw's crackdown.

In official statements, the Bonn government has disputed observations by West German commentators that West Germany is in danger of becoming isolated in its position on Poland not just from the United States but from the other West European allies.

Just as Schmidt was able personally to address Brezhnev on the issue of European-based nuclear weapons, so Bonn officials see potential gains for the West generally from a West German position that encourages leading Polish officials to stay in touch with them.

There are indications that Bonn is feeling the pressure from its allies to take a firmer stance, however. West German Foreign Minister Hans-Dietrich Genscher has put forward three conditions that must be met if the Communists expect Bonn to continue on its restrained course. These conditions are the lifting of martial law, the release of detained Solidarity leaders and others, and the resumption of talks among the party, Solidarity and the Catholic Church.

Repeating the conditions today before leaving for the European foreign ministers' meeting in Brussels and then a session with Schmidt and U.S. officials in Washington, Genscher seemed to be signaling for some gesture from Warsaw.

No deadline for a Polish concession was given, but one major West German paper today suggested that Bonn could not hold out without taking a stand on sanctions beyond the meeting of Western alliance ministers scheduled in Brussels Jan. 11.