ONE WOULD hesitate to say that kinship (they were cousins) is Anita Leslie's only claim as Randolph Churchill's biographer, but it is certainly the major one.

Leslie, whose father was a first cousin of Randolph's father, has written before about the Churchill clan -- a book about Jenny Jerome Churchill, Sir Winston's mother. But of the serious concerns of biography she seems to be largely innocent.

Which is not to say that Randolph is a bad book. It is, to the contrary, engaging in a gossipy, lady's magazine sort of way. But its striking quality is a point of view perhaps best described as Mitfordian: the light-hearted, entre-nous approach of Nancy Mitford's comic novels, Love in a Cold Climate and The Pursuit of Love. Nor is that wholly inappropriate, since Randolph Churchill was also kin to the unorthodox Mitford girls and in youth fancied that he was "in love" with Diana, later the wife of the British fascist leader, Sir Oswald Mosley.

Quotation marks are essential in the Mitfordian context: for whatever else the fluttery butterflies of Randolph Churchill's set might be called, or do, they remain in their essence English eccentrics. They might have posed, all of them, for various facets of Nancy Mitford's zany Matthew Radlett, who dressed his dogs in diamond collars to tease his neighbors.

As for Randolph Churchill, everyone knew that he was a brilliant, beautiful boy who never quite grew up, or lived up to the fond hopes of his doting father. He yearned to make his mark, as his father and grandfather had, in politics. But save for one wartime term in the House of Commons, which he served largely in absentia, the Tory party denied him the safe seat from which he could have execised his oratorical talent. So he had to content himself with journalism, Beaverbrook journalism at that, much of it mediocre. Meantime, he waited -- and waited! -- for Sir Winston to give him the coveted job of writing his life. How desperately he wanted the assignment, but he was too proud to push for it, Anita Leslie relates at length. What she does not quite explain is why Sir Winston hesitated until Randolph had practically drunk himself to death, or why he at last relented. By the time the task came his way Randolph's liver was nearly gone, and he lived to see only a couple of volumes through the press. Their high quality vindicated his dormant talents; but it was too late.

Anita Leslie gives a persuasive, often amusing picture of the qualities (especially loyalty and courage) that endeared Randolph to his friends (especially to several lady loves), notwithstanding a legendary rudeness that was exceeded only by that of his close friend Evelyn Waugh. (When surgery revealed that a tumor on Randolph's lung was benign, Waugh quipped -- at White's Club, the favorite hangout of both -- "So they've cut out the only part of Randolph that isn't malignant!") We are told of Randolph's mildly entertaining wartime exploits in North Africa and Yugoslavia, his gardening, his dogs, his battles with the pornographic press lords, his house, his travels, but the whole is somehow less than the sum of the parts.

WHAT WE are not told is anything of striking biographical consequence. The book is replete with such gossamer passages as, "To her eldest daughter Diana, Clementine was downright unkind and I remember . . . after Diana's first season Diana sobbed to me, 'I am so unhappy and Mummy is horrid to me because I haven't been a success, I have sandy eyelashes.' " There are curious omissions (or are they understatements?), as in this footnote: "Jack Profumo had caused the famous scandal in Lord Astor's house Cliveden when he was minister of war and he and Christine Keeler were accused of a swimming-pool flirtation." (Accused of a flirtation, were they? Ah, those naughty Cliveden weekends!)

Yet of course this comically personalized and myopic view of larger events would, come to think of it, reduce a major political scandal to tidy country-house dimensions.

Of the major forces that shaped Randolph's life and character, aside from the alleged coldness of his mother, there is nearly nothing. This, again, does not make Randolph a bad book; it merely makes "biography" a misnomer. It is more like a memoir. But even memoirs can be fine biographical portraits, as Violet Bonham-Carter showed years ago in her book on Randolph's great father. Anita Leslie is not the first, nor will she be the last, to take the fascinating Churchill family as her oyster, but she doesn't get much beyond the shell. She will never be accused of profundity, and indeed she often seems to confuse people with butterflies.