PARIS. — A FRENCH POLITICAL commentator recently suggested that 10 years is, so to speak, the ''consume-by'' date on politicians. Ten years, more or less, and British Prime Minister Margaret Thatcher was overturned. The students were in the streets against Gen. Charles De Gaulle a decade after he returned to power in 1958, and he was gone a year later.
The United States has written it into the Constitution. Just eight years and a president is out.
The pertinence of the French writer's observation is that within a few months Francois Mitterrand will have been president of France for 10 years. While his poll popularity remains reasonably high, against other politicians, the political classes are rumbling with discontent, and scandal after scandal turns up in public life, only to be stuffed back into corners or under covers. There is talk not only of end-of-regime but of end-of-republic -- and start of another.
There has always been a powerful current of hostility in France to the Fifth Republic's constitution, with its powerful presidency and weak parliament. Many would like a Sixth Republic, a new constitution, to make parliament supreme again.
This actually means return to the Third or Fourth Republics, when parliament dominated. The Third Republic has a bad reputation, chiefly because of its capitulation to the Nazis in 1940, but it lasted 70 years, from 1870 to 1940. The postwar Fourth Republic collapsed in a crisis brought on by the war in Algeria.
The record of both was of much government instability and political intrigue. The latter characterizes parliamentary and party politics today, to an extent which many find disquieting. Scandals over party financing and police and judicial manipulations fill the papers.
The institutional power of the presidency and of his prime minister -- who under the Fifth Republic's constitution can force laws through parliament without majority support (only a lost vote of confidence can really block the prime minister on a major issue) -- gives today's French government a stability and continuity it never had in the past. But there is resentment of the methods by which this is accomplished, as well as a sense of pervasive obstacles to change.
''La France s'ennuye'' -- ''France is bored'' -- was the famous title of a newspaper article on the eve of the upheaval of May, 1968. The French today give sign of being bored with Mr. Mitterrand. Mr. Mitterrand may be himself bored. His principal present interest appears to be to dictate his own successor, just as Mrs. Thatcher did hers, while undermining the obvious candidate, his own prime minister and old rival, Michel Rocard.
It does not seem to bother him, as it did not Mrs. Thatcher -- it surely does now -- that the first thing an anointed successor must do is break with his predecessor, so as to demonstrate independence. The British press still loyal to Mrs. Thatcher complains about John Major's ''posing as more compassionate and caring than his predecessor.'' This, The Sunday Telegraph writes, is ''distasteful'' and contrary to ''minimal standards of gentlemanly behavior.''
The French not only are bored but seem a little angry, in part because they find the opposition camp stalemated and hopelessly divided. The Socialist Party has broken into clans warring over the Mitterrand succession, but it at least includes several vigorous young candidates in addition to Mr. Rocard. The conservative opposition is blocked by the rivalry, now nearly 20 years old, between Jacques Chirac, mayor of Paris and former prime minister, and Valery Giscard d'Estaing, the former president.
Both are determined to run for president again, even though both lost the last time they ran. Neither will give up. Their rivalry, combined with the complications introduced by the competition of the extreme-right National Front Party, probably guarantees defeat for the opposition. If 10 years is the shelf-life of a serving politician, 20 years surely should be recognized as the date after which an opposition candidate has gone bad.
There are interesting young figures in the opposition camp too, who desperately form new movements and ''fronts'' and ''rallies'' trying to shake the old boys loose, but it never works.
The problem is that deeper things are going on here than the games of politicians. The Socialists were elected to national power in 1981 because they promised to make a radical change in how the French live. They did many good things, but they didn't do that.
Today they have nothing interesting to offer, nor does the opposition. The French like ideas. They need ambitious projects. The next national election is three years away. Local votes have shown unprecedented levels of abstention. Three years is a long time to go on being bored -- or apathetic, or angry. Of course there soon may be a war in the Persian Gulf to distract people. On the other hand, the French might at some point decide to invent their own excitement.