THIS IS a frivolous book, at times a silly book, and it is easy to see why art folk in New York and especially London have jumped all over it. The late Lord Clark was by far the best and most successful practitioner of >haute vulgarisation of art in our time and all time, both intrinsically better at it and affecting a far wider audience than his only real competitor, Andre Malraux. To have him subjected to Pop-shrink, which is the real content of this book, must seem intolerable. It is bad enough to have the process applied to artists, from Freud on Leonardo on down -- and that's the direction -- but to have it applied also and at great length to one whose only crime has been to write and talk about art more clearly and persuasively than anyone else does seem excessive.

They're right, those trans-Atlantic critics, but all the same, you do go on reading the book. Partly this is the popcorn effect -- you do go on eating it. Partly it's the morbid curiosity we all suffer from -- People magazine is a huge success. But also, like the curate's egg, parts of it are very good.

Lord Clark was surely best-known for his monumental and pioneering television series, Civilisation, and Secrest is suberb at re- creating the tensions generated by the experiment among the experimenters and at explaining the translation of discursive thought into visual thought, which was the heart of that series and the most important reason for its international success.

WHAT SHE is not very good at, indeed hardly tries to do, is explaining how Clark did what he did so well, making great art accessible to millions with no training whatever, just as it was for centuries before another kind of training in our own century made it into a mystery. At that point, which ought to be the heart of this book, Secrest retreats into reciting the superlatives of reviewers everywhere. What ought to be descriptive analysis of descriptive analysis becomes a quote ad.

What is really the heart of this book is a pair of revelations about the private lives of the Clarks which you will not find in his own immeasurably better written two volumes of autobiography. First, Jane Clark was a premature and inadvertent cocaine adddict and, later, a quite advertent drunk, falling down at parties, mucking up the professional life, the works.

Second, Kenneth Clark was a chaser. As soon as World War II took his wife and children off to the country, he began hitting the sack with every woman who came along, and they came along like streetcars, all named "Desire."

Natural talent or acquired taste, he never kicked his habit anymore than Jane kicked hers. There are times in the years in which he gained increasing fame that his private life seems like a Restoration comedy, even a Feydeau farce, with the hero juggling two or three women plus a wife simultaneously, all the while writing serious and excellent books, delivering sold-out lectures and demonstrating irrefutably that, regardless of the closet illiterates who run the American networks, you really can talk sense to a television audience if you do it right.

In Pop-shrink style, Secrest goes to considerable pains to blame the womanizing on the lack of love in her subject's childhood. The principal evidence for that, however -- being shunted off first to a nanny and then to a pre-public school at a very tender age -- applies to the sizeable majority of the British ruling class. The inference is too staggering to contemplate. There are easier explanations, beginning with our old friend, Hogamous, Higamous, Men are polygamous.

Secrest has some annoying mannerisms. Calling Clark "K" is okay: everyone did. But much more often she calls him "Kenneth Clark." In fiction you can do that to good effect, as Mann did in the The Magic Mountain, but with real people it sounds pointlessly pompous.

She's also pointlessly subjunctive a lot and occasionally raises false expectations: early on we learn that Clark's father was "the man who broke the bank at Monte Carlo." In fact we learn it twice, but we never learn when, with whom, how, or even if: she could have simply meant he was very lucky, not that, as the old song goes, he "walked along the Bois-de-Boulogne with an independent air." And, on the other hand, she can be unnecessarily instructive: "Dante Alighieri" (who needs "Alighieri" even less than Clark needs "Kenneth") is dutifully identified as "the fourteenth century Florentine poet." Oh! that's what he was. (Incidentally, Dante was at least as much a 13th-14th century man as Turner was "eighteenth/nineteenth," as he is here identified.)

If you have read all of Clark's books, seen Civilisation a couple of times and still want more, you can learn a good deal from Secrest: the details of the brawls at the National Gallery in London, the World War II British arts projects which led directly to the flourishing of the performing arts in a Britain otherwise in a state of decline ever since, other notes in the institutional art history of our time.

If, on the other hand, you have not read his books, you will profit immensely from reading them instead of this -- especially, in my view, Landscape Into Art in the revised edition of 1976, The Nude, available in paper, and >Piero della Francesca.

As a general antidote to this approach to biography, try to find The Personalist Heresy by C. S. Lewis, written by him as a scholar, not a theological sci-fi celebrity. It is a refutation of E.W.M. Tillyard's landmark book on Milton and powerfully presses the point that the works are hat count, not the life, however titillating.