WHILE MOST writers are still on their marks, Judith Krantz is half-way round the block. By the end of the first 20 pages of her latest novel, a customs guard has been lured from his duty with the promise of erotic delights and the Amberville family empire has fallen into the hands of the evilest uncle to stride out from behind the curtains since Claudius married Gertrude and drove poor Hamlet mad.

Not that Maxi Amberville is driven mad by the nasty and scheming Cutter Dale Amberville. Licentious lad though he is, Cutter is no match for the madcap Maxi, with her enormous wealth, jade green eyes and face which made "mere beauty seem not only irrelevant but uninteresting."

For years Cutter has carried around a heart heavy with hatred of his older and more successful brother. Now that Zachary Amberville is dead, Cutter can lighten up and begin the process of destroying his brother's memory.

As he begins to dismantle Amberville publications, he offers Maxi a lagniappe: the chance to resuscitate a dying magazine. Will Maxi, whose previous job experience lies in contracting improbably interesting marriages, succeed in saving the Amberville name? Will evil triumph?

You know full well it won't, but Judith Krantz makes the battle more fun than most. Her women have all the attributes necessary to a successful career in romantic fiction; they are beautiful, rich and desirable, and if they ever stare at their hair in the mirror and despair of split ends you won't read it here. The despair of a heroine is on a more cosmic order: love, death or the destruction of a financial empire.

And that, of course, is what Maxi despairs of. But what makes Krantz more readable than most writers trying to bring life to the body in the designer clothes is that her heroines have a sense of humor. Maxi, stumbling out of her first marriage, realizes that divorce'es in New York are as common as lint; she decides, instead, to be a widow. "She never left the house unless she was raven-clad from head to toe. . . . She learned to subtly sidestep all questions about her private life and automatically refused two out of every three of her many invitations. . . . Although she was deeply, constantly tempted, she never went so far as to tell anyone that Rocco Cipriani was dead -- stone cold dead -- but she never referred to a former husband, or a previous marriage."

The pseudo widowhood gives way to marriage to Bad Dennis Brady, whom Maxi meets when she considerately saves him from winning $40 million at the gambling tables. But soon life in Monte Carlo grows boring and a divorce takes Maxi from Bad to Mad, when she says "I do" to the daft Earl of Kirkgordon, who wanders out of his crumbling castle every day to spend six hours in the meadow practicing with his bow and arrow. Her decorators, receiving the latest call, despair: " 'What does Scotland mean to you, Milton? Besides deer stalking?'

" 'Cashmere sweaters, plaids, whiskey, ah . . . shetland sweaters, tartans, Drambuie, ah . . . haggis, bagpipes, trout . . . kilts! Leon, is this a quiz show?'

" 'Rain, cold, fog, wind, discomfort, lonely moors, the hound of the Baskervilles . . . ,' " intones his partner, who is, of course, right, and Maxi is off again.

THERE ARE two handsome brothers, one blind and one -- but no, that's a secret. There is a beautiful ice-maiden mother who melts into a passionate puddle when left too near a flame. A teen-age daughter (beautiful); a best friend (very beautiful) who is a famous but shy movie star and, at parties, "never carried a glass so that if she found herself stuck in conversation she could say, 'Oh, I must find a drink, I'll be right back . . .' If India actually wanted a drink she went to the bar, got it from the bartender, drank it straight down and gave the glass back, immediately."

What is the beautiful without the bad, and Cutter Amberville is a most satisfactory villain. There is nothing redeeming about him at all, the wicked wretch, and when he fails in the boardroom, he takes to the bedroom, so that I'll Take Manhattan does not lack for frequent and kinky sex.

It is an ideal book to buy now and save for summer, the right weight for a day full of sea, sun and sand and better than pretending for yet one more year that you are actually going to finish A la recherche du temps perdu.