THIS IS A LONG BOOK, but it is never tedious. It will fascinate not only people who still remember Noel Coward and not merely readers with a liking for gossip about show business; it will interest everyone who wishes to witness from within the process of becoming famous.

Graham Payn and Sheridan Morley have organized the available material with great skill. For the uninitiated they begin with a brief outline of Coward's life. This is followed by a prologue that races through his war years, during which the diaries are little more than a list of lunches eaten and celebrities encountered.

Thereafter time gradually moves more and more slowly until the diaries ceased at the end of 1969, three years before the dramatist's death. As we turn the pages, the entries become fewer but longer and deeper. We find beautifully written passages on such diverse subjects as a Billy Graham revivalist meeting, a pathetic Battle of Britain reunion, and the author's thoughts on his mother's death. There is something here much richer than the well-known bitchy emptiness of the plays.

It is engrossing to watch how, as Coward grew older, his awareness of the true function of a diary emerged. Everyone should keep a journal, but not so much in order to record mere events as to set down ideas and impressions with all the chaotic force they possessed at the time when they were formed. Autobiographers nearly always suffer from a tendency to shape the past, to justify it and to sheathe it in an unnatural consistency. In this book there are innumerable human contradictions. Vivien Leigh, for instance, is at one moment described as sweet and pathetic and, at another, as irritating in the extreme. Even England itself, which could once have relied on Coward's unswerving allegiance, finally lost his respect and came to be considered smug.

In Coward's day, nudity on stage was not a prerequisite of an evening's entertainment. Therefore at that time men never went to the theater gladly. At best they were their wives' muttering escorts, at worst merely their chauffeurs. In the '30s a theater-goer throughout the Western world was a middle-class, middlebrow, middle-aged woman usually suffering from a broken heart. These twilit beings Coward could shock or dazzle or console with consummate ease, but he soon became discontented with such a limited domain. The British press had a habit of comparing him with Ivor Novello and, to the annoyance of both playwrights, pretending that they were bitter rivals. In fact the paths of these two men seldom crossed and their aims were entirely different. Novello was a charming, handsome sentimentalist who lived entirely in and for the theater; Coward surveyed the scene through a wide-angle lens. He wanted to rule not only Shaftesbury Avenue but the whole world and, to an astonishing extent, he succeeded.

As is to be expected, famous names fall on to the pages of this book like tropical rain, but mention is made not merely of the most celebrated stage and screen actresses of his day (Greta Garbo is described as being "as bright as a button"). There are also references to kings, queens, dukes, earls, newspaper barons and prime ministers. Coward was not content with being presented to these illustrious personages; he played piano duets with the Queen Mother and croquet with Mrs. Churchill. He was even considered for work with British Intelligence in the United States, in spite of possessing so little tact that, during World War II, he made disparaging public statements about the behavior of G.I.s stationed in London -- an error that it took America many years to forget.

How did he achieve all this? Was he handsome? No. Was he lovable? Apparently not. He seems to have had constant squabbles with hs co-workers, and even his best friends were often subjected to pompous lectures about their behavior. He had what he himself called "a finger wagging" session with Marlene Dietrich. The nerve!

The shelves of bookstores throughout America have in recent times become weighed down with biographies in which authors claw at the still warm corpses of their victims. Even while, with our eyes bulging from their sockets and our lips glistening with saliva, we gloat over the revelations in these works, we despise ourselves. We need feel no such compunction when reading this book. The playwright condemns himself, sometimes with wry self-mockery, on other occasions in all innocence.

Coward was appallingly snobbish and surprisingly prudish. With the passing of time, his vocabulary became noticeably coarser but nowhere in his writings did he make any revelations of an intimate nature. In the few paragraphs which hint at his love life, the grammar is so ingenious that the gender of the object of his desire is concealed. He also hated outspokenness of any kind in others -- an attitude which caused him to disparage a number of his contemporaries, including John Osborne.

Patriotism might be considered by some people to be a virtue, but Coward carried this attribute too far: He was an imperialist of so fanatical a nature that, when Mahatma Gandhi was assassinated, his comment was "a bloody good thing but far too late."

Perhaps the nastiest of Coward's failings was his conceit. He seems sincerely to have thought that critics consistently gave his plays bad notices because they envied his success. The discovery of these flaws in The Master's nature in no way makes this book disappointing. On the contrary, it increases its fascination.

The answer to the enigma of Coward's popularity seems to lie in the modern word "charisma," which I take to mean the power to persuade without the use of logic. This quality the dramatist must have dispensed as the sun radiates heat. When, after a lifelong and often undignified screaming match with the British press, Coward returned to England from his heavily criticized tax exile in Jamaica, he was received with open arms. His 70th birthday was treated almost as though it were a coronation. The BBC gave him a party at which Lord Mountbatten and Sir Laurence Olivier made speeches in his honor. The National Film Theatre of London presented a season of his movies and the Phoenix Theatre staged a gala celebration of his words and music. To crown all this, he was at long last given a knighthood.

In youth the dramatist suffered a nervous breakdown and in middle age became the victim of lumbago, phlebitis and various other ailmants. Moreover he seems to have lived in a perpetual state of anxiety lest his flimsy singing voice should give out. Nevertheless, he wrote 50 plays, 25 movies, two autobiographies, a novel which remained on the best-seller lists for more than five months, and innumerable songs. With the other hand he presided over the Actors' Orphanage--a function which he took most seriously. In his spare time he painted enough pictures to be offered an exhibition and read what could hardly be described as light literature. He trudged through War and Peace and devoured all the works of M. Proust.

Perhaps, apart from the imponderable element of "presence," the main ingredients of success are a long life and indefatigable energy.