Europe lurched toward neutralism Sunday when this country elected a new president and West Berlin picked a new mayor. France dumped the most pro-American leader of the Fifth Republic, Valery Giscard d'Estaing, in favor of a Socialist, renowned for unreliability and heavily dependent upon Communist backing -- Francois Mitterrand. Berliners shook the coalition that supports the most pro-American leader in the history of the Federal Republic, Helmut Schmidt.

Washington, in these conditions, has to reassess the Atlantic connection. What follows is an analysis of the French choice in that context. Subsequent articles will deal with German politics, and the outlook for American policy.

France waxed fat during the seven-year rule of Giscard. Per capita income here rose faster than in any other advanced country except Japan. With growth went undoubted social progress. Good roads, an excellent rail system and modern telecommunications pulled even the most remote areas into the 20th century. A basic minimum salary was made available to agricultural workers. Bidonvilles -- the tarpaper shacks that used to house foreign laborers in every French city -- disappeared.

Almost alone among Western leaders, moreover, Giscard followed the Japanese example of systematically organizing the economy for competition in the international marketplace. He poured cold water on inefficient industries and fostered concentration among French firms in data processing. nuclear power, aerospace and sophisticated materials.

But the whole program was rammed down from the top. Technocrats in Paris managed the economy and made the big decisions. Giscard himself combined the technocratic approach with a cold snobbishness that kept him aloof from ordinary people. He thus became vulnerable to the dominant political force of the times.

That force, sometimes mistaken for a swing to the right, is populist resentment of centralized bureaucratic direction in the interest of modernization. It won elections for such disparate figures in such disparate countries as Menachem Begin in Israel and Maragret Thatcher in Britain and Ronald Reagan in the United States.

In France, it was mobilized during the first round of the presidential elections by the right-wing Guallist candidate, Jacques Chirac. It overwhelmed Giscard. It is typical that, apart from Paris and some conservative strong points, Giscard lost all provincial France.

Mitterrand, who is the beneficiary of the anti-Giscard vote, is anything but the Communist dupe portrayed by his enemies. Personally, he is as bourgeois as Monsieur Bovary. His record, at home and abroad, qualifies him as one of the most dedicated anti-Communists in this country.

He backed the Socialists in kicking the Communists out of the French government in 1947. He supported the Socialists in crushing Communist-led strikes in 1949.

Since those days, of course, Mitterrand has joined the Third Worlders in a general belief that the way to deal with liberation movements in Latin America, Africa and Asia is more by "social reform" than by application of muscle. Still, he denounced the Soviet invasion of Afghanistan in far tougher terms than Giscard, and equally the Soviet maneuvers around Poland. More than Giscard, he has openly supported the American effort to modernize European nuclear forces. Indeed, my private view is that Mitterrand counts as his chief objective in politics the crushing of the Communist Party and the development of a center-left majority.

At present, however, he lacks a majority in the French parliament. To get even a working minority, he will have to dissolve the National Assembly and hold legislative elections next month. The only way he can avoid defeat in those elections is to pool votes with the Communists in left-wing districts.

If that tactic fails, there will be a period of chaos, as for the first time in the Fifth Republic a president tries to rule with a majority in active opposition. Even if Mitterrand wins a working minority -- as he may, because of the bitter rivalry between Giscard and Chirac for leadership of the opposition -- a chancy period lies ahead. For the new president is committed to a program of economic stimulation bound to erode confidence in financial circles. And, with it, the prosperity of the seven fat years.

To be sure, Mitterrand is a supple politician. Many Frenchmen voted for him in the belief that, as one put it to me election night, "anything he promises to do he will surely not do." But even so, this country today recalls the comment of Louis Philippe that in France "anything is possible, but nothing can last."