Paris. -- Francois Mitterrand, France's president, has been called ''the Florentine'' because of the subtlety of his political perceptions and the deviousness of his maneuvers; and one must add, for his ruthlessness, which now appears to extend to a willingness to weaken the Fifth Republic itself for the sake of personal ambition.
His is a contradictory record with respect to the Fifth Republic's constitution, written and adopted under General de Gaulle. He first called it a mere subterfuge by which de Gaulle was discarding ''the last obstacles to his march towards absolutism.''
Mitterrand wrote in 1964 that the French people had before them ''simply a monarch, surrounded by his domestic servants; we have come to that.'' The Fifth Republic, he said, was ''a permanent coup d'etat.'' However, de Gaulle renounced power the moment the public indicated (in a referendum in 1969, on an unimportant issue) that they no longer supported him.
Twelve years later, Mr. Mitterrand was elected president of de Gaulle's Republic -- and did nothing to limit the powers of presidential office he previously had condemned. He reveled in those powers, and in the years after 1981 he personalized national decision-making to an even greater degree than had been the case under de Gaulle.
Time wears on politicians and their power, however, and Mr. Mitterrand, now in the fourth year of his second 7-year term, has fallen to his nadir of public sympathy (only 35 percent of the public expresses confidence in him, according to the latest opinion polls). He faces regional elections later this month and legislative elections a year from now. By every present evidence, his Socialist Party will lose both by crushing majorities.
He has made two responses to this. First has been to order his Socialist followers to direct their current regional elections campaign solely against the rightist National Front leader Jean-Marie Le Pen. The Socialists, directly or indirectly, have called people into the streets to block National Front election meetings, and this sometimes has ended in violence. Some Socialist mayors have refused to allow National Front rallies on public premises. Some Le Pen meetings have been banned by the government on the pretext that they jeopardized public order. There have been suggestions that the National Front be outlawed.
The purpose of this is to turn a vote which actually concerns local issues into a national referendum for or against Mr. Le Pen, RTC in which Mr. Mitterrand's ''presidential majority,'' led by the Socialists, presents itself as the sole alternative to the allegedly fascist National Front. The conservative parties who are Mr. Mitterrand's real opponents are supposed to be squeezed out by this tactic, which gives vast publicity to Mr. Le Pen and promotes the National Front as a force much more important than it actually is. (In the same national poll in which Mr. Mitterrand has only 35 percent approval, Mr. Le Pen has 12 percent -- and 80-percent disapproval.)
Mr. Mitterrand has indirectly promoted the National Front for many years through election-eve statements about votes for immigrants or relaxed immigration rules, designed to send frightened conservative voters into the overtly anti-immigration Le Pen camp, thus weakening the legitimate conservatives. It is clever, in a brutal way, but it also is dangerous. Mr. Le Pen now is the most prominent rightist figure in Europe, and for this he can chiefly thank President Mitterrand. The two have suited one another very well.
The president's second maneuver has yet to take place but is being pressed upon the Socialist Party's leaders -- not all of whom are pleased by what is contemplated. Mr. Mitterrand wants to install proportional representation for the next legislative election, in 1993. This is the only way he sees to keep the conservative opposition from dominating the National Assembly.
Full proportional representation, on present computer simulations, would bring so many National Front and ecologist deputies into the National Assembly that the democratic right would only be able to form a majority by allying itself with the National Front. Mr. Mitterrand, on the other hand, could reasonably expect to dominate the Assembly on most issues through shifting majorities drawn from the Socialists, Communists, Greens and Centrists.
For all practical purposes, this means recreating those Third and Fourth Republic conditions of parliamentary intrigue and weak and short-lived governments which the French repudiated under de Gaulle, by adopting the Fifth Republic constitution.