The late Philip Williams used to remind his students in French politics that Paris, in the days of the Third Republic, had 75 separate lemonade vendors' unions. No such society could be expected to conform to neat Anglo- Saxon standards of political tidiness.

The muddled state of French affairs following the recent National Assembly elections suggests a resurgence of the lemonade vendors' instinct, repressed by nearly 30 years of Gaullism. It had been Charles de Gaulle's intention to put France on easier terms with strong, stable government. His Fifth Republic constitution, written and adopted by plebiscite in 1958, featured a presidency modeled a bit on our own but elevated (as de Gaulle himself was) above the partisan fray.

What we have now, thanks largely to Francois Mitterrand, is a president of one party and a National Assembly (and prime minister) of another.

As Americans know, it isn't essential for presidents and legislatures to be of the same party. It is helpful if they are at least of the same persuasion; and in France at the moment they certainly are not.

To be sure, political upheaval in France is never so drastic as it may seem to outsiders -- neither Mitterrand's socialist victory in 1981 nor the present revolt against Mitterrand's failed policies. Whatever the flavor of the regime, Napoleon's great centralized administration, constantly replenished by bright recruits from the Ecole Normale Superieur, runs the country like a clock.

De Gaulle understood all this, but never made peace with it. He never forgot (nor forgave) how the bureaucracy accommodated itself, with scarcely a flutter, to German occupation in 1940.

As for "the politicians," as he scornfully called them (in his own eyes, he was quite above politics), their infantile games were damaging and insulting to the eternal France. As de Gaulle saw it, the mercurial parliamentary coalitions of the '40s and '50s (17 governments in 12 years) could never make hard, incisive decisions.

Inflation, France's place in the European community and in the East- West struggle, the future of the rebellious colonies in Algeria and Indochina, the technical and economic future -- all these vital issues had been shelved, because government was too feeble to deal with them. With the brief exception of Pierre Mendes-France, no French prime minister had made a real choice since the war.

In 1958 there occurred the ultimate paralysis of parliamentary coalition government: an army mutiny in Algeria threatened to plunge the nation into civil war. De Gaulle took charge by near-universal acclamation and proceeded to write his long-held views into a new constitution.

What he clearly did not intend -- and it didn't happen as ong as de Gaulle and his prot,eg,e Georges Pompidou held the office -- was the conversion of the Fifth Republic presidency into just another politician's perch, where power could be manipulated in the name of some transitory ideological fancy.

But that is precisely what Francois Mitterrand and, to a significantly lesser degree, Valery Giscard d'Estaing have done with de Gaulle's imperial presidency, to its serious injury.

Mitterrand politicized what de Gaulle intended to be a sort of democratic emperorship. He has undermined the logic of the Fifth Republic and thrown France, once again, to the lemonade vendors -- the eternal anarchist in every French voter.

Although repudiated in the elections, Mitterrand has contrived a slick formula for his own survival, one an advertising agent might have thought up (and perhaps did). He calls it "cohabitation," a new term whose French overtones are presumably not so ribald as those of the same word in English.

However ambiguous the Fifth Republic constitution may be, "cohabitation" is a perversion of de Gaulle's design -- the intentions of the framer. De Gaulle would have deplored Mitterrand's embroilment of the presidency in programmatic politics, socialist at that. He would find it astonishing that having done so and failed, Mitterrand clings to the shell of a vanished authority.