BOOK REVIEW : There’s No Avoiding Love in the Big Apple : GUEST OF A SINNER, <i> by James Wilcox</i> HarperCollins $20, 278 pages

People out here who are homesick for New York will love “Guest of a Sinner.” It’s about sex, God, unhappy families, but most especially--how to hold on to a rent-controlled apartment.

This novel by James Wilcox will also help to explain to Los Angeles-lovers why New Yorkers are so homesick. We live out here in an anonymous city. New York (the place in this book anyway) is as tight and dirty and cramped and soiled and solid as a beggar’s cyst. Put another way, the characters here are thick as fleas: they can’t get away from each other; they literally keep jumping into each other’s space.

Eric Thorsen, a serious, semi-successful classical pianist in his early 40s, has the looks of a Greek god but has never married. Although he’s thoroughly heterosexual, he has an ice queen attitude: Get away from me! I’m so beautiful, I’m so snippy! You can love me, but you can’t touch me! An attitude like this doesn’t take anybody very far, and Eric, beautiful as he is, is out of his mind with loneliness.

He’s also being driven stark-staring mad by the woman in the flat beneath him who keeps more than 50 cats. The stench from all these kitties wanders handily up the air vent to Eric’s place, so, fleeing from ammonia fumes, he’s been driven to live temporarily with his older sister Kaye, a large, meddling, gregarious woman in her 50s who lives a disappointed life as a saleslady in Macy’s basement.

She has domestic troubles of her own, because their father, Lamar, also meddling, gregarious and vague, has moved in temporarily with his daughter because he’s lonesome and afraid of dying all by himself. Pouting, impossible Eric has blamed his father for years for driving the car in which his beautiful mother perished in an automobile accident. He’s at his wit’s end with exasperation, having to live with Lamar and his sister.

All of these characters are Catholics and part of their ongoing urban quest is to find the perfect church, preferably where no one will ever recognize them.

Eric, in particular, can’t stand any person that might require his “Christian love.” He’s irritated beyond words one morning when Wanda, a spinsterish 41-year-old, gallops up to him after Mass and thrusts a novel about lesbians into his unwilling hands. Wanda is mad for him, of course, but feels strongly that the subject of this novel will keep him from thinking that she’s an “aggressive” woman.

Many other people wander through this cluttered New York cityscape: a menacing woman behind the notions counter in the skyscraper where Wanda works who calls everyone “Doll”; a rosy little gent who has recently left the priesthood and used to have a big crush on Wanda; also, Wanda’s demented uncle, who has been tactfully asked to leave the priesthood after an “unfortunate episode” with a few altar boys.

Wanda, as it happens, is housesitting for her boss from a small foreign country who employs her to--all unknowingly--pirate everything on television for later sale in his own Third World land. Eric wants no part of this silly project, and no part of Wanda either! He can’t stand little mousy blondes who follow him around.

But when he’s with Wanda, things keep getting out of hand. Eric picks up vodka bottles and drains the contents; he starts smoking again, three packs a day! He falls asleep leaning against Wanda on a couch; he falls asleep in her tub, dead drunk.

This is a time-honored story about the conventions of love set in a moderately gruesome context: The turgid waters of daily life don’t always part for the focused journey of two lovers who must, must, come together. Eric’s sister Kaye is outraged that her brother has fallen in love; his father is crazy with irritation and scorn that Eric’s gone around the bend over this pokey little woman ! The rosy pink-cheeked man who’s left the priesthood mysteriously disappears; the demented uncle who had that unfortunate incident appears . The lady with all the cats is taken to court.

Everyone here ends up very happily, and the best part of all, when absolutely everything is said and done, there seems at the end to be one or two or even three relatively new, absolutely usable, attractive apartments in the extended family, and they’re all rent-controlled.