THE ENIGMA of Francois Mitterrand has been a constant in French political life since World War II, when he escaped from a Nazi prisoner-of-war camp and became a chief of the underground Resistance. A minister in the Fourth Republic at age 30, he has been in constant public view and debate since then, moving relentlessly through political parties he has helped create and kill off, through collapsing cabinets, and through long periods of lonely opposition, toward a single goal -- the French presidency.

And yet, when he was awarded the Elys,ee Palace last year by an electorate disgusted with the regal mannerisms and aloofness of Val,ery Giscard d'Estaing, Mitterrand remained something of an unknown even for many who voted for him and his Socialist Party. Behind the apparent candor and constant public engagement lies a private Mitterrand who shields his inner feelings and beliefs with the furtiveness a man would have learned in Stalag 1515.

France's importance in today's nuclear politics has made the study and forecasting of Mitterrand an international game as well as a purely French pastime. The publication here of his two best books in a single volume entitled The Wheat and the Chaff will provide some help, although ultimately Mitterrand's elusiveness again wins out.

Mitterrand has produced a rare political book -- one that is nimble, enjoyable to read, not obsessed with settling scores, and, when he is writing about the French countryside he knows and loves, poetic and moving. In typical deceptive fashion, he advises the reader to consider these clean and finely drawn sketches of people, places and ideas that he encountered in the 1970s simply as "jottings," rather than as memoir or journal.

Evidently by design, he emerges from these pages as erudite, sensitive, solitary and a person who likes to travel. When Mitterrand has a spare moment, he takes down the three or four atlases he keeps to "compare the various colors and typefaces that make the same country seem so different, and I make up all kinds of itineraries . . . I love to read a country's fate in the map of the world. Minor game, major game, depending on the choice."

Mitterrand's reflections, which benefit from an excellant translation, were composed between 1971 and 1978 and here are grouped chronologically. The reader goes along as Mitterrand rebuilds the Socialist Party through constant voyages abroad, vigorous polemical writing at home and the fashioning of an electoral coalition with the French Communist Party to oust the center-right establishment put in place by Charles de Gaulle.

Mitterrand displays a grudging admiration for de Gaulle, whose towering shadow lies across the early part of the book. There is a strong hint that Mitterrand feels that through their generation-long rivalry he came to understand de Gaulle better than anyone else. It is natural, therefore, that he would eventually inherit and know how to use the political institutions of the Fifth Republic crafted for de Gaulle.

He does not mask his resentment that de Gaulle led the fight against Hitler from London while he and others fought in clandestinity at home in "a fight whose glory I felt, was being taken away from the people -- of whom I was one." But he acknowledges that "de Gaulle-as-hypothesis, by becoming reality, erased competing ones. . . ." The general became "a man who throws himself across the path of destiny, seizes it by the throat, forces it to change its path, and creates, by virtue of his forewarning and will, a new path for it to follow."

Perhaps the most revealing political insights offered here come in the glimpses of the Soviet Union and its Eastern European satellites provided by Mitterrand. The Russian leaders and ideologues that he meets are sinister and their portraits suggest why Mitterrand has taken such a stern anti-Soviet line in the early days of his seven-year term. The men in the Kremlin remind him too much of the teacherous French Communist leadership he has had to deal with at home -- and they have nuclear missiles at their disposal.

After years of listening to "Communist officials, from the most modest secretary of the most modest cell to the secretary general of the party" begin every discussion by reading a carefully prepared text, Mitterrand looks forward to his April 27, 1975, meeting with Mikhail Suslov, "the guardian of theory, the prosecutor of deviation." The top ideologue in the Kremlin "rubs his beautiful arthritic hands together, blows his nose, shrugs his shoulders, consults his companions, loses his temper" as he talks to Mitterrand -- and reads "practicallly everything he said. His text was written on large sheets of copybook paper. . . . It is wasted effort, for Suslov himself -- even Suslov -- reads!"

"Like all popes of transition, Brezhnev wants to hang on, and he is hanging on; braced against time, he endures. His power comes from instablity and he wields it through equilibrium," Mitterrand wrote seven years ago.

If he reacts politically to the Soviet Union, Mitterrand reacts emotionally to the United States, which he has called that "vast continent, quite incomprehensible." Standing on the 65th floor of Rockefeller Center, he watches "wild ducks banking at 80 miles an hour over the prow of Manhattan" and sees a vision in December 1975, in which "America is in the brink of something impossible to imagine. Too many blows received have made her huddle in her corner like a groggy boxer . . . But wait till she rises to her feet once more and heads for the center of the ring."

On that visit heegoes to see Henry A. Kissinger at the State Department and finds him to be one of those men who "take pride in forcing history to march backward." America's policies and institutions are detached from its own values, and he observes of Kissinger: "An unplanned policy can take as its point of reference only 'Realpolitik,' whose very nature it is to copy what has been done before."

The people whom Mitterrand openly likes probably tell us more about him than those he distrusts or fears. Golda Meir entrances Mitterrand, telling him, "As I was born in Kiev, King Khalid (of Saudi Arabia) thinks I am a Communist. Whatever you do, you can't change it -- a Jew will always be held responsible for his birth." And he gets along well with Carlos Rafael Rodriguez, a master story teller and a Cuban Communist who refused to join the party in denouncing Fidel Castro before the Cuban revolution. "He became Castroite without ceasing to be Communist, while waiting for Fidel to become a Communist without ceasing to be a Castroite."

There are other stunningly good sketches, of Harold Wilson forgetting the title of a book he had written and that Mitterrand admired; Nicolae Ceaucescu, the president of Romania, who "literally chews up his words . . . His face is dead serious, his features chiseled, and his head sunk into his shoulders. You feel he is crouching, attentive, vigilant, leaving nothing to chance, the mortal enemy of political careers in this part of the world"; a Mao who is "of medium height, wearing a gray Sun Yat- sen uniform, one shoulder lower than the other, slow of step, his face round and peaceful, short of breath and soft of voice . . ."; and many others.

Most of all, it is the portrait of France which Mitterrand draws that counts. He is passionate in describing her virtues, and the faults that he attributes to the country's wealthy class and its political servants. The political sense he portrays here has little to do with Marxist ideology or any other doctrine, and everything to do with a sense of injustice that is historical rather than "scientific." He is still outraged that right-wing French parties collaborated with the Nazis in World War II. He blames the right for France's disasters of 1848, 1871, 1914 and 1940, which he lays at the door of a "bourgeoisie which has no policy -- not even in foreign affairs, where the safety of the country is at stake -- save that of protecting its own class interests."

It is against this "right wing which calls itself 'national' and wishes to monopolize the brand name and vintage 'France' " that Mitterrand has gone to political war. "I have seen enough miserable lackeys of the German occupation straighten up again in the Gaullist takeover of 1958, seen them drink and eat and sleep again, urinate red white and blue, and berate the Left in the name of national interests which they alone seemed to understand."

It was through such passionate opposition that Mitterrand defined himself over the past two decades. He has continued to hug the shadows now that he is in power. But France's economic stagnation and the growing loss of confidence in the Socialists' political program are forcing Mitterrand to make the more difficult choices of responsiblity and to define himself as a man of action. The results remain highly uncertain. But The Wheat and the Chaff suggests that at the least we can expect a good book from Mitterrand out of it all.