HOW TO MAKE enemies and still be loved.'' That could be the subtitle of this biography of the most charismatic of modern French politicians after De Gaulle. No one speaks of Pompidou or Mitterrand in the tones of almost religious awe that are still used of Pierre Mendes France.

The reason is not that he was a financial whiz-kid. When he was still only 31, in 1938, he was chosen to virtually run the country's economy. In 1943 De Gaulle appointed him his minister of finance. But it was not because he performed economic miracles that he had his extraordinary reputation. It was the sort of man he was.

He was a religious phenomenon, more than a politician. He was not impressive to look at, short, pale, an eternal five o'clock shadow. He was not particularly charming, except to his close friends; even with them he could be harsh and obstinate, lose his temper, drive his audience to distraction with his relentless arguments: ''I shall never again,'' said De Gaulle after one meeting with him, ''allow anyone to speak to me for three hours about economics.''

His passionate conviction that he was right was combined with an instinct for unpopular causes that he sensed the public secretly approved but dared not adopt. Mendes France had courage to the point of being willing to be a martyr. His program was austerity, honesty, refusal to compromise, the union of politics and morals. This is not usually the way to political office, but it can be to a certain kind of power over public opinion. There was never a Mendesist party, and he was never truly at home in any of the parties he supported. His legacy is ''Mendesism,'' which remains a nostalgic dream for many French people, the vision of a utopia in which reason triumphs over passion.

The contrast with Mitterrand is striking. Mendes France recognized that he himself did not possess the lobbying skills a conventionally successful politician requires. In 1954 he brought Mitterrand into his government for the express purpose of remedying that weakness; when it comes to parliamentary management, he said, Mitterrand was ''like a pianist at a keyboard: he knows everybody and everything.''

Mendes France was widely regarded as General de Gaulle's natural successor. But it was Mitterand who stepped smartly in to declare himself candidate for the presidency, and to point out that Mendes France was, for all his qualities, impossible, because he had offended too many pressure groups. Mendes France (like De Gaulle) wanted to be drafted by the force of public opinion, recognized as inevitable. He was perhaps even more intransigent than De Gaulle; he was the doctor who offered France the most bitter-tasting pill, and who insisted that was the most powerful medicine. As one of his colleague said, Mendes France was very intelligent, but he lacked common sense. So he was, in all, prime minister for less than eight months, called to office in desperation to do the impossible, to carry out the inevitable unpopular amputations, and then quickly got rid of.

The politicians feared him as a potential providential man, to whom France might entrust its destinies. But he won a rare kind of admiration outside the narrow circles of parliament, a deep devotion, that gives him still a special place in the country's memory. He is one of the great noble failures, like the hara-kiri heroes the Japanese like to admire, too brave, with ideals too lofty for ordinary people to emulate.

I met Mendes France myself only once. It was deeply moving. There was an unfathomable well of sadness in him. The way he married pessimism with idealism was one of his great attractions. He was unprotected by the normal thick politician's skin: one could almost see his bones through the mantle of loneliness and disappointment he wore: he radiated a strange combination of modesty and strength.

BUT it was not the public's admiration that sustained him. He always felt he was not liked. When discussing the attitude of other politicians and journalists towards him, he would recall little incidents at length, and always draw the same conclusion: ''You see, I am not liked.''

In only one way can he be said to be a prophet before his time. He drank milk, not wine. How could such a politician hope to succeed in the land of burgundy and bordeaux? He would have a better chance today. The latest statistics say that only a minority of French people still regularly drink wine with their meals (46 percent). Twenty-two percent are now teetotalers.

The publication of this highly intelligent, well-informed book is also a sign of changing times. The French have never gone in much for biography in the past. Jean Lacouture is an exception. He has not, it is true, written a biography in the Anglo-Saxon style: he quotes from speeches rather than from correspondence, he is interested in public events, not private life (with only a few sentences, for example, about Mendes France's two wives: he does not give their view of the man). But he has the advantage, as a top journalist, of having followed Mendes France's caree over many years, sympathetically and perceptively: he knows how to make the reader share in the tension and identify with the tragic elements of the drama. At times, this book reads almost like a thriller, even though we know, almost from the beginning, that the victim is doomed by his exceptional qualities, and we watch horrified as he accumulates different kinds of rope to tie round his own neck.