I'LL TAKE MANHATTAN. By Judith Krantz. 437 pages. Crown. $18.95. THE thing to do is to be positive, to look for the good in Judith Krantz's new novel, ''I'll Take Manhattan.'' Don't go searching for blemishes. Never mind that on page 3 beautiful Maxime Emma Amberville is described as moving ''with the tadpole agility of the born New Yorker'' as ''she slapped her shoulder bag down on a customs table and looked around impatiently for an inspector.'' It makes perfectly good sense if you don't stop to think about it.
Never mind the implausibility of the 1945 scene in which Maxi Amberville's father demands a copy-boy job at The New York Times and is turned down by ''the Times receptionist,'' who suppresses ''a giggle'' when the applicant expresses his disappointment with an obscenity. I'm sure Judith Krantz has a couple of believable things to say about the New York publishing industry, providing you don't examine them too closely.
Remember that books respond to trust and affection. If you like and believe in them, they'll repay you 10 times over in ways you'd never expect. Sometimes, if you listen carefully, they'll even tell you their story. ''I'll Take Manhattan'' is such a book, and while the tale it tells may be a predictable and cliched one of a magazine empire threatened by the bad brother of the good brother who built it and its rescue by the good brother's dynamic daughter, the tadpole Maxi, there is this to be said: You wouldn't learn it if you didn't read it. All it takes is a little patience.
Try to see the good qualities of ''I'll Take Manhattan.'' For instance, you're never in doubt when a new character appears in a scene. You know he or she has put in an appearance in the way that you would know it if you were standing in a room and a hand grenade without its pin were rolled in. Here's how Cutter Amberville, the bad brother, is insinuated into our awareness. ''He had changed surprisingly little during all that time, never losing the spare fitness of the superb athlete he was. His still-blond hair was closely cut, his gaze a slash of blue, his manner never less than disarming. He was a compellingly alluring man who had bewitched many women, yet there was a darkness of some inner purpose in his manner, a hint of something hidden. He seemed to have little need for humor or for people whom he didn't find useful.'' Hisssssssssssss.
Look, Mrs. Krantz has studied up for this book. She's learned about the New York magazine industry and how one of the best spots on the newsstand in the Pan Am building is right next to Cosmopolitan. She's learned about Manhattan real estate and that the second best apartment in Trump Tower is ''an 'L' and an 'H' thrown together,'' or so says a character in the book named Donald Trump.
She's learned about the ''disease of retinitis pigmentosa'' that has made the eyesight of Maxi's brother Toby ''increasingly limited.'' ''Was his tunnel vision still relatively stable? Maxi wondered. It was never easy to know what Toby saw or didn't see since one of the characteristics of his disease was that his vision varied from hour to hour, depending on the set of conditions in which he found himself, the distance and angle from which he looked at something, the brightness or dullness of the light, and a dozen other variables that had a maddening inconsistency so that at times he had moments of accurate seeing which only made the return of his condition of near-blindness more difficult to endure.'' O.K., I'll bet you Mrs. Krantz knows more about human sexual organs than most of us do. At least she imagines more.
Let's face it, any book can run into a bad patch of weather and get blown off course. Just because Mrs. Krantz hasn't mastered certain refinements of telling a story doesn't mean that her novel doesn't deserve our love just as much as ''Anna Karenina'' or ''The Wings of the Dove.'' ''I'll Take Manhattan'' is a novel too. In fact, it deserves more love, because paradoxically, it's the unlovable who need our affection most. Its fierce needs make us close our eyes to its weaknesses, especially the inability of its creator to stick to a consistent point of view, so that there's no logic whatsoever to its narrative, or any rhyme or reason to the timing of its revelations.
It has its good points too. And not less than an hour's careful reflection will reveal them to us as the dawn does the landscape of the new day's horizon. Let's see: how about the idea that Maxi finally comes up with for a new magazine that makes women feel good about themselves instead of guilty? How about the stuff on retinitis pigmentosa? Well, did you know that the second best apartment in Trump Towers was an 'H' attached to an 'L'?
Listen, ''I'll Take Manhattan'' is no worse than Judith Krantz's other novels, ''Mistral's Daughter,'' ''Princess Daisy'' and ''Scruples.'' And those were just as good as a dozen other novels I can think of that have climbed the best-seller lists and been made into television mini-series.
At least it's better than a stick in the eye.