THE BEST chefs of France have a persistent worry: The loss of a start in the Guide Michelin, the gourmet bible followed docilely, followed quasi-religiously, by the vacationing palates and pocketbooks of Europe and the U.S. It is, professionally speaking, the worst blow that can happen to a virtuoso at the stove, and it can happen.

"Chef So-and-so has lost a star . . ."

The most complacently successful cuisinier experiences a visceral reaction at the mere thought, conjuring images of the public fall from grace, of the humiliation and diminished influence that the omission of a minute symbol in a pocket guide book can effect . . . to say nothing of the significant loss of clientele (a projected 33 percent) once the initial blow has been weathered.

In the past, certain chefs have solved radically the problem of survival after the fall.

Charles Barrier, the "alchemist of Tours," however, is a different kind of man.

Barrier, called the "self-effacing mentor of the nouvelle cuisine movement," was sitting in his living room in Tours when the word came through last March: His restaurant, Barrier, after 11 years on Michelin's list of best houses, had been stripped of that all-important third star.

(The reclusive Barrier, who rarely gives interviews and who is always eschewed the usual publicity tactics, lives in a small bungalow a short drive from the banks of the Loire amidst a jumble of cookbooks dedicated by junior confreres.

("To Charles Barrier . . . my best friend and the wisest of us all. Paul Bocuse."

("To Charles -- our example. Pierre Troisgros."

("To Charles, maitre of us all. Michel Guerard.")

How would this 63-year-old "chef's chef" -- in the kitchen for more than half a century -- accept the news that for him, the nightmare had come true?

Intimates were concerned. It is more or less open knowledge that in 1974, the "perenially anxious" Barrier had contemplated suicide after losing a son in a car accident.

His reaction to the Michelin decision, however, was as unconventional, as fresh and unpredictable, as his numerous innovations at the stove.

"It was a hard blow," recalls Barrier, sitting in the same living room nearly a year later. He is small, intense man, an avid student of philosophy who has the look not of a cook but of a scholar.

"It was, as they say, the worst thing that could happen. But when the worst does happen, you discover something important. You learn that we all have resources inside us which we never dreamed were there. In 10 seconds my decision was made."

What decision was that?

Barrier pauses a minute before replying.

"Why to begin all over again," he exclaims, "to start from scratch. From zero. After all, a man is either passionne (impassioned by his work) or not worth bothering about."

The plan, to sweep away all things status quo and to begin fresh, went into effect immediately.

"You know, I should send a thank you letter to Michelin," adds the chef ingenuously. "I have never been more exhilarated in my work, never lived more intensely than I have lived this year."

Most Michelin demotions are predictable, within professional circles, at least. When Maxim's was stripped of a star in the '78 guide, few in the metier were surprised.

The Barrier demotion, however, came as something of a shock to a number of his peers in the kitchen.

Among the puzzled were Jacques Lameloise of Chagny and Gerard Boyer of Reims, the two young chefs who won their third Michelin star in the very 1979 edition which stripped Barrier of his. Both new three-star cooks, during the heat of a personal triumph, took time out to wonder aloud over the demotion of their confrere in Tours.

"In the kitchens of France," they ventured thoughtfully, "before a star is lost, there is always talk. With Barrier it was different. There was no talk at all. That silence made the Michelin verdict somehow more disturbing. tChefs have been wondering why. We all know that there have been family problems at Tours. And Barrier has that mercurial temperament. He has no public relations veneer. But he is one of the great innovatore. And those of us who know him, know what he has done and is still doing, are asking ourselves, 'If Charles Barrier is not a three-star chef . . . then which one of us is?'"

"The morning after I heard the news," recalls Barrier, "I played what I call my game of poker. I made an all-or-nothing decision. It meant riding headlong over family considerations. It meant telling my son Francois that from here on it would be me at the stove all the time again. Not an easy verdict for a young man to hear.It meant telling Nicole that I wouldn't be seeing her or the children very much. It also meant instructing the serving staff not to make the most minor decision without consulting me."

"It was a big risk," he reflects, "the brigade, and the family, could have cracked there and then. But we didn't.

"Now," continues Barrier, "at an age when most men are thinking of retiring" (he will be 64 next month) "I am back to 7 a.m. to 2 a.m. days in the kitchen. The regime is taking its toll on family life. The physical effort is super-human. I come home each night with my shirt soaked through, drying on my back, thinking, My God, if my health can only take it! But it's been nearly a year now, and I'm still alive."

One of the interesting facts of life concerning Michelin Guide strategy is that while the book decrees, it never explains. A visit to guide headquarters in quest of information is rather like a one-man effort to storm the Bastille. iThe building at 46 Avenue de Breteuil is solid and imposing. A guard signs you in. You are then escorted by elevator to a bare parlour on the second floor -- one table and plain wooden chairs.

Enter Michelin spokeswoman Madame Reboul, dressed with matronly severity, in keeping with the company's tone.

The object of the visit? To ask: "Why Barrier?"

Madame Reboul is all courtesy. She finds any number of diplomatic ways to phrase the inevitable answer: No comment.

"Why are stars lost? It is not our role to provide a commentary. The reason, however, is not always found in the kitchen. Why Barrier? We do not give out such information. We are a guide. We don't pretend to be anything else. Decisions, final ones, are in the hands of the guide's editorial director. We never justify them. And we don't give out his name."

Madame Reboul is good at her work. It is safe to assume that in her years with Michelin, she has never lost a round.

In his living room in Tours, Charles Barrier is reviewing the year of his lost star.

"The work has been exhausting," he ruminates, "but the rewards have surpassed everything. When you are at the stove without respite, you can control each detail, because you have no middle man working as an interpreter. Morever, you get bored quickly. You change a lot. I find I am changing everything all the time.Yesterday, for the first time, I made a sherbet of rosemary and one of linden. I have been experimenting, too, with an infusion of elderberry. I have observed that the seeds of the flower, if you picked them on the eighth day, give out a special taste of honey."

Traces of science again. Barrier haas always been interested in the scientific aspect of the kitchen.

"For more than 20 years," he recalls, "I have been working with a scientist friend in his laboratory in Tours. Together we have manager to leaven breads with fermented fruit juice -- grape, pear, apple. We have distilled linden honey vinegar, and have been working on methods of cooking with cold, as opposed to heat; carrots cooked by chilled, salted water, cucumbers cooked by ice. We have distilled an eau de vie from rose petals, and another from the buds of cassis. These days, we are working on methods of leavening bread, with wild yeast from a well-aged loaf, as peasants did years ago. The bread is already on the table of my restaurant."

Michelin's chief rivals, Christian Gault and Henri Millau, the powers behind the Gault Millau Guide to France, sit side by side in their office on the Rue du Faubourg St-Antoine, much as they sit side by side at the table on several book covers. Perhaps as a foil to Michelin's Olympian remoteness, Gault and Millau have chosen an informal, subjective approach to restaurant evaluations which certain professionals find even more disconcerting than the Michelin stone wall.

Henri Gault is conversing with Switzerland by telephone. It is Christain Milau who attacks the subject of Barrier.

"The Barrier decision," he repeats. "We found Michelin's action inexplicable and, in a sense, brutal. We can't understand why they did it, and we haven't hesitated to say so openly."

Openly -- and more than once.

"Forget about the fear and the worry caused by the loss of a star of one of our old confreres," reads their recently-released 1980 guide.

"More enthusiastic and more of a perfectionist than ever . . . the youngest 64-year-old cook in France is off again to even bigger things . . . You will discover a new Barrier, anxious as always, but full of marvelous ideas -- a man at the high point of his career."

In Tours, the afternoon has passed quickly.

"My life has been different from that of most chefs," recalls Barrier over an orange juice which remains on the table, untouched. "I didn't have a father in the metier to help me out . My mother was a widow with a large family. We grew up in a cave dwelling in the village of Cinq-Mars. Times were hard. We literally didn't have enought to eat. There were several Barrier families in the village. To distinguish us we were called 'Les Barrier Misere' -- the destitute Barriers.

"When I was 12, on July 14, I won the prize of excellence at school. Two weeks later, my mother said to me, 'Now, we must find you work.' I'll never forget it. She was a proud woman. She put on her Touraine national costume, the great white bonnet, the embroidered apron, and she took me on the train for the first time in my life to Tours.

"We went to a hotel. I was clutching at her hand, trembling like a leaf. 'Will you take my boy?' she asked. The manager looked at me with disgust. 'He is too small,' he replied, 'he is too thin.' We went to five, then six hotels. Finally, a cashier, a woman, looked at my mother hard. She had understood. She took me out of pity.I was left there alone, the mother's boy who had never been so much as a night away from home.

"Often I trembled physically like a little animal over the next years. I was a little animal. I hated it. It was the epoque in the kitchen of the 'coup de pied' (the brutal kick with a wooden-soled 'sabot'). It was not until I was 18 that I felt a trace of human warmth in a chef. I was working in the kitchen of the prince of Monaco. From the first, an electric current passed between up. 'What do you want to do?' he asked me. 'You must learn to love your work!'

"It came as a revelation.That man made me see that this, the kitchen, is a metier noble, a means of expressing everything. Becuase of him, I became passionne."

Barrier has been "passionne" every since.

"At 35, I was obsessed," he recalls. "I could work three days without sleeping, catnapping on a chaise lounge next to the pastry oven. My kitchen was a laboratory. I was rethinking concepts, developing ideas. One day I was ebloui , dazzled by a concise formula of St-Exupery. Listen to it: 'Art isn't when there is nothing more to add -- but when there is nothing more to take away.'

"That was when my long work of elimination began -- the demi-glace went, and also the butter-flour thickeners. I worked with egg yolk liaisons only, thickening sauces by emulsion. Nowadays all of these nouvelle cuisine principles are accepted. A quarter of a century ago, they thought that I was crazy.

"You know," concludes Barrier, "I think back on those days when I slept by the stove and than I look at my life today, with its 18-hour schedule, and I realize that I am as obsessed as ever. I have never lived more intensely than I am living now."

The new Michelin Guide, 1980 edition, is about to be released.

A last question for Charles Barrier, the anxious alchemist of Tours: After his all-or-nothing campaign of this year, does he expect to win back that third crucial star?

Barrier's face closes shut.

"Never," he replies, shaking his head slowly, "Michelin will never ever give me back my third star."