West German Chancellor Helmut Schmidt Monday becomes the first Western leader to visit Moscow since the Soviet invasion of Afghanistan, causing nervous U.S. officials to wait anxiously for the outcome of the two-day talks.

Schmidt is expected to hold discusions with Soviet President Leonid Brezhnev on Afghanistan, disarmament and dentente in Europe, following up a metting between the two leaders in 1978 in Bonn.

This meeting is a much more risky one, set against a rupture in East-West relations and placing into jeopardy Bonn's own relations with Washington for unlikely major concessions from the Kremlin.

The chancellor's interest in the trip is chiefly to demonstrate his belief that East-West communications must be maintained during serious periods of tension. Aides to Schmidt say they expect no breakthrough from the talks, but argue that the trip can serve to clarify positions and reduce the danger of miscalculations. It is also thought that the visit will be seen by West German voters as a popular peace gesture in an election year.

Because of the delicacy of the mission, Schmidt has taken pains in recent weeks to plan the brief summit carefully and with considerable public comment, an approach clearly in contrast to the surprise meeting last month beteen French President Valery Giscard d'Estaing and Brezhnev in Warsaw.

Carter administration officials, while never openly objecting to the Schmidt trip, have appeared concerned about its timing and real purpose, worried that it may add to the appearance of the Europeans' carrying on Business as usual with the Soviets.

The talks reportedly were the subject of a contentious letter from Carter to Schmidt earlier this month, which resulted in a display of public irritation between West Germany and the United States.

Schmidt has taken both the recent Venice seven-power summit meeting and the NATO foreign ministers' conference, at which Western allies were briefed about the West German leader's trip as encouragement for it. In addition, President Carter last week endorsed the talks.

Schmidt also has said that he will not be going to Moscow as an emissary with any sort of mandate from the Western alliance, nor will he serve as go-between for the United States and the Soviet Union. Rather, he has said he is going to pursue West Germany's own interests.

These include expanding economic ties with the Soviet Union and more relaxed relations with East Germany and the Soviet Bloc countries, as well as a heightened interest in European disarmament negotiations.

Schmidt has said he will tell Brezhnev that the Soviet occupation of Afghanistan is unacceptable and that Soviet troops there must be withdrawn completely. He also will urge the Soviets against deploying nuclear weapons targeted on Western Europe. The chancellor also intends, however, to reaffirm Bonn's interest in cooperating with the Soviet Union.

In addition, Schmidt plans to raise in Moscow three or four points at the request of President Carter. The speculation is that Scmidt might sound out Soviet officials on the U.S. suggestion that Moscow consider a phased withdrawal from Afghanistan.

The chancellor is under pressure from the conservative Christian Democratic opposition to achieve concrete rusults in Moscow on the Afghan crisis, disarmament and human rights.

Opposition leaders have warned that the trip could be seen as weakening the Western stand and have cautioned Schmidt against empty displays of statesmanship for election purposes.

Concern for what Schmidt might say to the Soviets on disarmament was the source of the sharp exchange this month between Schmidt and Carter. In a letter to the chancellor, Carter called into question Schmidt's support of a NATO decision last December to station nuclear missiles in Europe capable of reaching the Soviet Union to offset buildup in Soviet nuclear forces.

Schmidt has proposed that East and West agree not to deploy these weapons for three years -- the time it would take the United States to produce and prepare for installation of the weapons -- and proceed instead with negotiations to limit the number of them.

At first, U.S. officials feared that Schmidt's proposal would undermine the original hard-won NATO decision. After conferring last week in Venice, however, Carter and Schmidt said there were no differnces between them on this subject.

What still worries Washington, according to U.S. sources, is that the Soviets may decide to accept Schmidt's proposal, thus weakening Western resolve to go ahead with deployment of the missiles.U.S. sources also think that perhaps the Soviets will float a tempting offer of their own. "The Soviet leadership may make him an offer he cannot refuse," an American source in Bonn said.

An opposition Christian Democrat summed up the concern this way: "He will go to Moscow with empty hands and return with them tied behind his back."