BOOK REVIEW : Evil Seen Through Upper-Middle-Class, Myopic British Eyes : THE GATES OF IVORY, <i> by Margaret Drabble,</i> Viking, $22; 462 pages

“The Gates of Ivory� is an ambitious, well-intentioned (some might say pretentious) novel about the juxtaposition of two worlds that seem never to mesh. Margaret Drabble at first invokes these separate modes of being as “good time� and “bad time.�

In terms of geography, they divide down to East and West; civilized--if shabby--England, and the oft-evoked Orient, particularly Vietnam and Cambodia. In England, evil has been whittled down and privatized, as exemplified in the person of serial killer Paul Whitmore. In Cambodia, as we know from newspaper accounts we do not really understand, evil has been legalized and made public, under the fearsome regime of Pol Pot.

Yes, it’s true that Pol Pot has been pushed out of Cambodia by a Vietnamese occupation, but the Vietnamese and the Cambodians dislike each other intensely and with the collusion of former Prince Sihanouk, Pol Pot plans a return that we in the West may be unable to comprehend.

Would Cambodians prefer a mass murderer of their own to the unfeeling rule of the Vietnamese? And how is the Western mind to understand the misery, the disastrous life, of the Cambodian refugees in the camps along the Thai border?

With all the news that has been disseminated across the Western world, nothing so far has made the Cambodian killing fields accessible to souls comfortably ensconced in Merry England.

Margaret Drabble’s set of upper-middle-class English men and women seems particularly dim about the suffering in other lands. “The Gates of Ivory� is the third novel in her trilogy about middle-class life, and her characters are, by now, middle-aged and set in their ways.

They form a small circle of friends and have, by now, managed to conduct affairs with most of the people they know, or have married and divorced each other a couple of times. Their hous es are comfortable, their cars expensive, their gardens weeded and in bloom.

Thus, when Liz Headleand receives a mysterious package from Cambodia (or Kampuchea as they call it now) containing the effects of her old novelist friend Stephen Cox, Liz remembers that, yes, Stephen has announced his intention to voyage to Asia (to write a play about Pol Pot), but when was that, exactly?

She phones one of her best lady friends, Alix Bowen. Alix can’t remember either. Liz calls up Hattie Osborne, a ditzy bohemian who’s subletting Stephen’s flat, and she does remember when last she saw him, a couple of years ago, but remembers it only in terms of how drunk she was. In other words, Drabble’s English characters appear here shallow to the point of cretinism.

They are far more ignorant than, according to their circumstances, they should be. They don’t read Joseph Conrad, they don’t care about politics, they can’t understand French; they’re dopes, and Drabble has no use for them.

Stephen Cox, who has already won the Booker Prize and has a decent career, journeys to the East for reasons he can’t put into words. He needs to face evil--those killing fields, the indescribable poverty and sadness of “Bad Time�--but he is distracted on his way by a beauty queen named Miss Porntip, who manages to get a cocktail named for him in a tourist trap hotel.

This is the “East� we like to think about, Drabble suggests: the land of pretty girls and Singapore Slings. We don’t like to think about death, whether it be Pol Pot’s genocide or Paul Whitmore’s murders and eventual botched suicide attempt.

This should be a major novel because its subject is transcendentally ly major. But the author sabotages herself by her own bad humor. She draws her characters with such condescension that when they begin to sicken and die, the reader feels nothing at all.

That may have been Drabble’s intention and appropriate to a book about mass murder, but as a novel it inevitably ends up as a spinsterish sermon.