IN HIS SECOND book of short stories, A Time to Dance, Bernard Mac Laverty recalls the fears of childhood and imagines the indignities of old age. This Ulster-born writer, now living on the Isle of Islay, explores the world of the very young and the very old, the innocent and the helpless. His best stories map out a frightening terrain where the inhabitants smash up against reality.

The collection's best story, "The Beginnings of a Sin," traces the disenchantment of a fatherless Irish altar boy named Colum. Called a "creeping Jesus" by his older brothers, the child has the ardor of a very young and very earnest soul. He idolizes an old priest, failing to see, as every villager knows, that the man is a sot. He misinterprets the symptoms of the priest's alcoholism as signs of a special sanctity: "Colum always wondered why Father Lynch was so nervous saying his morning Mass. He had served for others and they didn't tremble like that. Perhaps it was because he was holier than them, that they weren't as much in awe of the Blessed Sacrament as he was."

Mac Laverty deftly fuses Colum's religious yearnings and his earthly concerns. At one point, the boy lovingly compares his rosary beads to a measuring device belonging to an older, admired brother: "Where the loop of the beads joined was a little silver heart with a bubble of Lourdes water in it -- like the spirit level in his brother's tool kit." After Colum sees the priest so drunk that he falls and rams his head against a radiator, his awe turns to contempt, and his energetic, breathless faith is blighted as well. Colum has joined the villagers.

This theme of knowledge blasting innocence runs throughout Mac Laverty's work. His first novel, Lamb, chronicles the warping of a pure love between a Dublin slum child and a teaching brother. The motif reappears in "A Time to Dance," the title story of the collection.

Set in a Scottish strip joint, the tale recounts a fateful noon. We wait with a small boy locked up in a broom closet. Outside his mother peels off her pasties to the accompaniment of a hooting crowd quaffing its liquid lunch. The boy gleans his mother's true occupation by peering over a crate onto the strobelit runway. He realizes he will never again see her in the same way. Using the language of a child, Mac Laverty conveys the lad's desolation. To punish himself, the boy yanks off an eyepatch he wears to correct lazy eye, "thinking that if he was going to become blind then the sooner it happened the better."

Mac Laverty's compassion extends to the aged as well. In "No Joke," we encounter an old man as he arises on his 83rd birthday. Watching the dawn, he tries to recall some snippet of Baudelaire's poetry he once committed to memory. The retired headmaster of a parochial school, Frank Stringer valiantly attempts to stave off mortality. His effort has included 20 years of "calisthenics," and a daily performance before the bathroom mirror as he shaves: " 'Angry employer,' he said. 'Jones, you should have been here at nine o'clock,' he changed the tone of his voice to a piping treble, 'Why, sir, what happened?' His shoulders began to shake up and down but the sight of himself laughing in the mirror always brought it to a stop. It was the same with crying."

Relegated to an Irish day-care center for the elderly, Stringer still clings to his wit and dignity, even as the nuns introduce new patients as "our little friends." But a fog of senility mists over his intelligence; verbal slips and physical frailty expose the decay of age. We witness the man's helplessness, and shudder for ourselves. Once again, knowledge torpedoes innocence. If age can ravage this man with his exercises, his erudition, and his humor, what fate aw homoaits us?

Like most short story collections, A Time to Dance offers a mixed grill. Mac Laverty is best when he writes of masculine youth or old age. The three stories told from a feminine viewpoint lack a clear tone. The reader does not experience a twinge of recognition.

The best stories, "A Time to Dance," "The Beginning of a Sin," and "No Joke," though, erase the memory of a few false notes.