"An historic event," former chancellor Willy Brandt cabled lyrically in congratulating Francois Mitterrand on his election as president of France last Sunday. But Helmut Schmidt, the present chancellor, spoke of the need for an early meeting and "deeper discussions."

The difference in tone reflects a difference of outlook that divides Germans at a time when, having again lost their bearings, they are once more on the prowl for new combinations at home and abroad. So the coming of a Socialist to the presidency of France has an impact across the Rhine that is bound also to engage relations between the superpowers.

Prosperity has been the West German religion since the inception of the Federal Republic back in 1949. For years the steady accumulation of economic power eclipsed the itch to reunify the country split asunder by World War II. But now the German economic miracle is wearing thin. This year, growth is negative, and unemployment is on the rise. Foreign trade, the motor of the German economy, is in deficit for the third year in a row.

Disturbing portents of social disorder -- a new stirring of the German soul -- have recently come from many quarters. In most of the major cities -- in Nuremberg, Dusseldorf, Hamburg, Munich, Stuttgart and West Berlin -- defiant youngsters have taken over empty buildings in a "squatters' revolt." Protests against construction of nuclear power plants have disrupted the national energy program. The most popular film in the country is "Christine F.," the story of a teen-age prostitute hooked on heroin.

General unrest has worked to undermine the authority of the governing coalition led by Chancellor Schmidt. Within his own Social Democratic Party there has developed a left-wing opposition centering around Brandt. The Brandt wing wants to stimulate the economy more, push forward to detente with Russia and enter more actively into economic cooperation with the Third World countries of Africa, Asia and Latin America.

But Schmidt cannot make accommodations on the economy without affronting his coalition partners -- the Liberals led by Foreign Minister Hans-Dietrich Genscher. In foreign policy Schmidt and Genscher have worked out with the United States and the outgoing French President Valery Giscard d'Estaing accords for modernization of nuclear weapons in Western Europe, and for an application of some muscle -- as well as economic cooperation -- in the Third World.

The vulnerability of the chancellor to his internal opposition found expression last Sunday in elections in West Berlin. That city, a Socialist fief for 35 years, has been governed for the last 11 by a coalition of Socialists and Liberals. But this time the Socialists were damaged by a scandal, and outflanked on the left by and "alternate list" of squatters, environmentalists and left-wing Socialists.

In the election, the "alternate list" picked up 7 percent of the vote. The Socialists and Liberals both lost heavily. The opposition Christian Democratic party will probably form a new government with an assist from the Liberals. That new coalition could serve as a model for an early change of regime in Bonn itself.

Two issue engaging the superpowers become salient as the chancellor struggles to prevent further erosion. One is the modernization of nuclear weapons favored by Washington and bitterly opposed by Moscow. The other is policy toward the Third World. The United States seeks, and the Russians oppose, German support for operations to contain left-wing influence in Central America, the Middle East and the Horn of Africa.

The France of Giscard tended to tilt the Germans along lines favored by the United States. Mitterrand does not have clear policies on either of the salient questions. But he will need Communist support to govern France. His ties are with the Brandt wing of the German Socialists. Most of his advisers strongly favor the Third World. Far from being a bulwark of support for Schmidt, as Giscard was, accordingly, Mitterrand deals cards to the chancellor's enemies.

So May 10 was Black Sunday for the chancellor. The elections here and in West Berlin provided two or more manifestations of a negative trend. Unrest in the Federal Republic has been given new life. The chancellor will be under increasing pressure to yield to his own left wing. The Russians will be all the more tempted to fish in the deep waters of the German soul. Washington, as it prepares to receive Schmidt next week, will find it that much more difficult to manage relations with the country on the edge of the East-Wing divide that has increasingly become the European anchor of the Atlantic connection.