Books: The Banality of Deceit OTHER PEOPLE'S WORLDS

OTHER PEOPLE'S WORLDS by William Trevor; Viking; 243 pages; $10.95

William Trevor is an Irish-born novelist and short-story writer highly regarded for the had understated manner in which he suggests that quot;real life" and other a illusions may be dangerous to one's health. His deadpan style disguises a compassion for the peevish, the confused and the lonely. The Old Boys (1964) and The Boarding House (1965) had funny moments; yet the novels' deeper impressions were made by sympathy for the elderly and middle-aged attempting to preserve a fleeting respectability. The Love Department (1967) rollicked along on the efforts of a lovelorn columnist to stamp out adultery, but the book is remembered best for a punishing point: seducers can be staggering bores. The abysmal selfishness suffered by the unloved haunts Trevor's previous novel, The Children of Dynmouth (1977), in which a 15-year-old boy turns into a blackmailer.

That little monster appears to have grown into Trevor's newest menace, Francis Tyte, 33, a bit-part actor, pathological dissembler, bigamist and homosexual prostitute. Tyte's face, lean and handsome in the Leslie Howard mold, is known to millions of British telly viewers. He is the fellow in the tobacco ad who nonchalantly puffs a pipe while military officers strut by, sniffing.

At one time or another, a number of people believed that they knew him better. A 50-year-old dressmaker in Folkestone married Tyte in 1965, let him do the shopping and the housework and then threw him out for unspecified acts. He then enchanted two elderly sisters in Cheshire, moved in with them and stole their money. In London he seduced a shopgirl who, twelve years after she bore his daughter, still hopes he will marry her.

As Other People's Worlds opens, Tyte's meandering trail of deceit has taken him to the Gloucestershire town of Stone St. Martin, where he is engaged to Julia Ferndale, 47, widow of an army officer. The japonica is blooming, the folk politely buzz about Julia's young semicelebrity, and her mother, Mrs. Anstey, reads Dickens and feels vaguely uneasy about her future son-in-law.

With good reason. Behind his boyish smile, Tyte is one of the crawliest characters in recent fiction. He specializes in making a mockery of privacy. "Make-belief is all we have," he tells another actor, a woman who plays the part of an infant murderer in a television play. Tyte's personal script usually starts with the story that he was orphaned when his parents were killed in a train crash. In truth, Mom and Pop are in a retirement home that Francis never visits. Having eased his way on sympathy, he plays it by ear and keeps an eye open for opportunities. " 'You'll bring your dragon brooch?' he said, speaking of their honeymoon. 'And your little sapphires and your seed pearls?' Surprised, Julia replied that jewellery could be a nuisance when you were travelling. 'I want to show you off.' sHe smiled at her."