West German Chancellor Helmut Schmidt this week begins his seventh visit to Washington since taking office, and all indications are that this trip will rank among the toughest.

Schmidt, who arrives Tuesday evening and will meet President Carter Wednesday, is expected to be pressed on the one hand to put more concrete measures behind his government's repeated professions of solidarity with the United States.

On the other hand, however, the West German leader is expected to resist any action that would place his country in direct confrontation with the Soviet Union.

This means, among other things, that Schmidt can be expected to stall further on a public decision now to boycott the Moscow Olympics in retaliation for the Soviet invasion of Afghanistan even though informed sources say he will assure Carter privately that Bonn will not send its athletes to Moscow if Washington does not.

An aide to Schmidt said West Germany opposes the U.S. idea of organizing an alternative to the Moscow Olympics. "It is not an ingenious idea," he said, explaining that such a move might put unnecessary pressure on Third World countries that already have expressed alarm over Moscow's incursion into Afghanistan.

Schmidt and other European leaders have agreed to delay an Olympic boycott decision until May 24, to allow for the possibility that the Soviets will begin to withdraw their troops.

West German and U.S. officials appear to differ somewhat in their assessment of Soviet intentions in this regard, with Bonn more willing to test recent Soviet statements reaffirming a desire to withdraw, provided the West ceases its "interference" in Afghan internal affairs.

Schmidt is expected to discuss with Carter details for setting up a negotiating mechanism through which the European-sponsored notion of a neutral Afghanistan might be achieved.

Should the Soviets not be out of Afghanistan by the time Bonn must decide about the Olympics, Schmidt hinted last week that the West Germans would not participate. His top aides say, in stronger terms, that participation in such a case would be inconceivable.

Nevertheless, Schmidt is anxious to avoid any action against the Soviets that would risk unraveling the delicate web of relations Bonn has spun with Eastern Europe over the past decade -- web that is the showpiece of Schmidt's Social Democratic Party and one the 61-year-old chancellor must defend in national elections this autumn.

Perhaps the most significant result of this policy -- over and above the increase in trade and repatriation of thousands of ethnic Germans from of East it has brought -- has been a general lessening of tensions in Central Europe.

The Afghan crisis and resulting chill in East-West relations clearly has heightened insecurity among West Germans, according to recent public opinion polls. Indeed, in sharp contrast to the surge in fighting mood in the United States the public mood in both Central and Eastern Europe has been running scared.

This difference goes a long way to ward explaining Schmidt's low-key response and his reluctance to sound alarms. While Carter stressed punitive measures. Schmidt promoted a longer term policy of Soviet containment and strengthening ties with the Third World.

Schmidt is said by aides to have been particularly displeased with Carter's Feb. 20 Olympic boycott ultimatum, viewing it as an overreaction that limited East-West maneuvering room. Furthermore, there is still concern here that the United states will be led into a new arms race, although Schmidt reportedly has found encouragement in Carter administration statements in favor of continuing detente.

"The auspices for the visit are good," said a Schmidt aide, adding, "I did not say bright, but good."

Washington has been encouraged by some steps Schmidt has taken recently as part of West Germany's attempt to demonstrate that it is a loyal American ally. The chancellor has declared publicly that Bonn will increase its defense budget by 3 percent in real terms this year, as Washington has urged, and would consider other measures, including economic sanctions against the Soviets.

Schmidt's statement on sanctions, however, carried the condition that all Western nations and Japan agree to go along. Furthermore, his fresh pledges of solidarity with the United States have been carefully coupled to warnings against an escalation of East-West tensions.

Schmidt's strengthening of Bonn's commitments -- punctuated by timely praise of President Carter for showing "exceptional statesmanship" in his handling of the Iranian crisis -- appear aimed at removing friction so that he and the president can focus on Afghanistan without further irritations within the alliance.

On another front, Washington has been urging Bonn to limit its export credit guarantees for trade with the Soviet Union as a gesture of economic solidarity. In recent days, Schmidt has reaffirmed support for expanding the so-called Paris COCOM list governing the sale by Western allies and Japan of strategically important goods to the East. He also has signaled support for shorter credit terms to the Soviets, provided other allies go along.

The key to Schmidt's strategy for responding to Afghanistan, however, remains a long-term package of joint Western measures -- including aid to Turkey and Pakistan together with initiatives in the Persian Gulf and Africa -- and defined by a "division of labor" among Western allies.

Despite recent private expressions by Schmidt of annoyance with Carter over a lack of sufficient consultation, the chancellor's biggest problem has not been with Washington but with reaching a consensus for action within the European Community -- with France in particular often going its own way.