THE SHORT STORY, at its best a tight and resonant form, is good at rendering the eruptions of hope and eccentricity which can transform constricted lives.

William Trevor's stories are especially successful at this, for he is a writer whose sympathies lie with the elderly, the gentle and the timidly brave. A moving example is te title story of his new collection. It is about a London love affair of the '60s: a wistful idyll "touched with the same preposterousness" as the frenzied decade itself. The man, emblematically named Norman Britt, is a married and moneyless clerk and the only place he can find to make love to his girl is a hotel bathroom at Paddington railway station. Marble-walled, "like somewhere in a palace," it is little used and in it the two find illicit bliss. Sneaking up there during their luncheon breaks, they eat their sandwiches among incongruous splendors which typify the folly of their long-term hopes. They lack the stamina to fight Norman's wife, and later Norman will look back on the affair as on "a fantasy that bad miraculously become real."

Looking back is a thing which characters in all these stories do. The book's title is ironic, for few of them care for the present. Some suffer from it; others retreat into folly or fantasy but the author himself confronts it with a cold, Prufrockian eye. His people are defined by their temporal props, hedged and shackled by specific (often lower-middle-class) realities. Trevor is a moralist, and there is a hint of the ascetic in his emphasis on physical impedimenta. Carnal greed is a characteristic of our day, and it is significant that Norman's barren wife should be "unduly demanding" in bed." 'Feeling fruity, dear?' " is her come-on phrase and her reaction on learning that he loves someone else is to feel " 'switched. . . on.' " Norman's dream of love and babies is beyond his means but kinky sex is an amenity of our time.

An Irish writer living in Devon, Trevor is alert to the quirks of people on both sides of the Irish Sea and extends compassion both to the politically troubled Irish and to an England which he sees as succumbing to armies of careless, self-righteous innovators. Bullies and bigots of every stripe draw his fire. In one story, an Irish women living in London is horrified that her accent may make neighbors think she condones the random bombings by her IRA compatriots. "She felt she should have been out on the streets, shouting. . . that the bombers were. . . despicable. . . . But she was not that kind of woman."

Nor is Trevor that kind of man. His mode is devious. Brashness is repugnant to him.Significant images and telling details are the weapons he uses to nail his targets. One of these, a schoolmaster who picks on an elderly widow for "an experiment in community relations," sends children "from broken homes" to redecorate her flat, ignoring her protests that she likes it the way it is. The children, who arrive with blaring transistors, do not hear her either. They spill paint, slap garish colors on her walls and make use of her bedroom because " 'We needed sex.' "The story is a bristle of camouflaged comments. One is in the title: "Broken Homes," another is in the way the teacher makes a "mush" of a biscuit the old lady serves him by dipping it in his coffee. His mind too is a mush of undigested slogans.

Trevor's comedy is as muted as his commentary. In "Attracta," another Irish story, an old Protestant teacher recalls having seen sectarian hatred fade in her lifetime. Now it has flared again, yet she tells her pupils not to despair, finding hope in bleakness, just as the author finds humor in her memory of the town bigot's cornering her when she was a girl and using flasher's vocabulary to warn her against Catholic friends: " 'Has she tried anything on?" he asked. 'Has she shown you rosary heads?. . . Look away immediately if she gets them out of her apron or anything like that'."

The most ambitious piece in the book is "Matilda's England," a trilogy of stories, dealing with the evils of nostalgia. Here too an old person talks of the past to a child. Mrs. Ashburton, owner of a decaying grand manor in Dorset, has "caught a mood" from her husband who was shell-shocked in 1917 and communicates it to Matilda, a girl from a local farm who later grows up to marry the son of a man who "made a killing" in munitions in World War ii. He installs her as mistrss of the manor but, sour in her obsession, she makes him pay for the war, the Ashburtons' loss and for the fact that, "Nothing is like it was."

More than the other stories here, this one reads like an allegory of England today, where nostalgia is often felt with keenest resentment by those who could not have expected to inherit the lost grandeurs if they had survived. The story could be read either as a lament for the death of an upper class or a reverie on the dangers of storytelling. I enjoyed puzzling over its protean meanings and found Matilda credible. However, it lacks the impact of the other stories. Paradoxically, Trevor's talent seems to sharpen under the challenge of depicting the new England he deplores and becomes blunted when dealing with lost grace.