THE MOST DANGEROUS place to be, in Ian McEwan's fictional world, is in between the sheets. At the end of "Pornography," the first story in this new collection, a cocky young man named O'Byrne finds himself strapped to a bed, awaiting castration at the hands of his two lovers. In "Psychopolis," the last and best story in this book, Terence falls in love with Sylvie and offers to prove his devotion by doing whatever she asks. Sylvie responds by ordering him to urinate in his pants in public.

Terence never winds up in bed with Sylvie. But not so fortunate is the heroine of "Dead as They Come." This story is almost an allegorical guide to McEwan's work. It can be read as a comment on male attitudes toward sex, as well as a gruesome example of the materialization of love. In it, a rich man falls in love with a mannequin, his "Helen." At the story's climax (the structural pun would seem to be intended), the man rapes and kills Helen. He enjoys an orgasm as she is dying. He then goes on an orgy of destruction: "I tore, trampled, mangled, kicked, spat and urinated precious possessions."

Throughout these stories, sex is an invitation not to love, but to violence. It is a weapon used to exert power over others, to possess and objectify them. Love becomes an infantile and destructive force, a source of humiliation.

McEwan is a satirist in the tradition of Nathanael West. His stories focus on the extremes and exaggerations of human behavior. McEwan seems to feel that to write of ordinary people would be pointless - such an approach would be boring. No one would listen. This attitude is revealed in another scene from "Psychopolis": an amateur stand-up comedian, at a nightclub for would-be entertainers, tells the sad, depressing story of his very ordinary life. The story is not funny, and the audience is indifferent. The point is that the citizens of the "city of narcissists" are numb to commonplace human suffering. Only extreme, perverted pain attracts attention.

Most mainstream art, McEwan, seems to suggest, does little to wake people up, to get through the numbness. In "Dead as They Come," the rich man reflects on his beloved, "I saw once more her genius for wearing clothes. I saw beauty in another being as no man had ever seen it, I was art, it was the total consummation of line and form that art alone can realize." Beauty, art, and genius are all here associated with a character who is literally a dummy. Art is something unalive. Beauty is reduced to fashion.

Faced with this kind of situation, McEwan turns to tales of rape, mutilation, and murder. (And, If we include his first two books, incest can be added to the list.) But he is not heavy-handed. His stories are complex and his prose, like Orwell's, is as clear as windowpane. (In fact, one story, "Two Fragments: March 199 - ," is indebted to Orwell in style and subject matter.) And McEwan's comic edge gives these stories a moral force. They are not meant simply to shock and horrify middle-class readers. Rather, like all good satire, they seek to unmask hypocrisy and cruelty.

In its original meaning, the word "person" meant "mask." People are actors. They play many different roles and wear numerous disguises. Mary, in "Psychopolis," says, "Everyone here has got some kind of act going." This tension between people and the roles they play is a dominant interest in McEwan's fiction.

One of McEwan's favorite techniques is the use of role reversals. In his fictional world, children are often more mature than adults. Many of his child characters are in the "14 going on 40" category.And some of them - e.g., Charmian, a little girl in the title story, who has a bullet-shaped head, a double chin, a "bullish" neck and a faint moustache - are frightening. Men are frequently "the weaker sex," as the unfortunate O'Byrne discovers in "Pornography." And an animal, not a human, is the most articulate and sensitive character in any of these stories (read "Reflections of a Kept Ape").

Ian McEwan is a gifted story-teller and possibly the best British writer to appear in a decade or more. His first collection of stories, First Love, Last Rites (1975), is a brilliant, obsessive book. His only novel to date, The Cement Garden (1978), is that special kind of book that's difficult to tear oneself away from. If some of these new stories seem more strained than his earlier work, it is because McEwan is experimenting more with the elements of his fictional world.

That world is a disturbing one, and hard to characterize. McEwan knows about perversion - spiritual as well as sexual. Susan Sontag wrote, "Real art has the capacity to make us nervous." In Between the Sheets is definitely real art. CAPTION: Picture, Ian McEwan by Jerry Bauer