THE STORIES OF MURIEL SPARK. Dutton. 314 pp. $18.95.

IN 1951, six years before her first novel was published, Scottish-born Muriel Spark won an Observer short story competition. She produced more short stories early in her career than late, although she continues to write them, and they were gathered into two collections, The Go-Away Bird in 1958 and Voices at Play in 1961. This was the period in which she also wrote such fine short novels as The Comforters (1957), Memento Mori (1959), The Ballad of Peckham Rye (1960), and The Prime of Miss Jean Brodie (1961). (Two other volumes published in Great Britain, Collected Stories I and Bang-Bang You're Dead remixed and reprinted earlier work.) Now 27 stories -- the contents of the two early collectons plus some other and more recent pieces -- have been gathered into The Stories of Muriel Spark, and it is as impressive and enjoyable a volume as anyone could wish for.

Spark is not a flashy writer. Her prose is clean, modest, unfussy, casual, almost offhand. Remember when she wrote the climactic line, "Well, there was a Miss Jean Brodie in her prime," and we knew exactly what she meant. Frequently, the dominant tone of her work is one of wistful reminiscence. Almost always, the voice is highly personal, and it is no surprise that 19 of the 27 stories here are told in the first person.

This unmannered, very civilized voice is a suitable and very flexible instrument for Spark. It can sound perfectly innocent when in fact it is most knowing. It can mention insignificant bits of data that will explode noisily later on. It can speak of the fantastic -- ghosts, visions, supernatural threats -- and still sound eminently sane. And all it qualities -- the calm, the self-control, the decency -- serve to highlight Spark's consistently dark themes.

Many of her characters could agree with the narrator of "The Twins," who observes, "I am too much with brightly intelligent, highly erratic friends." And many, like her, watch and observe and then draw back from the unpleasantness. "I sent myself a wire that morning," the narrator reports, "summoning myself back to London." But she does not fail to report, quite objectively, the nastiness she has witnessed.

In "The Go-Away Bird," young Daphne, "delighted and amazed to be grown-up," finally succeeds in leaving Africa to live in the England of her dreams. She lives for two years with a novelist, then later returns to Africa and dies. Soon after, the novelist is seeking a subject for a new book. "He ranged his experience for a tragedy. He thought of, and rejected as too banal, the domestic ruptures of his friends past and present. He rejected the story of his mother, widowed young, disappointed in her son, but still pushing on: that was too personal. He thought of Daphne. That might lead to something both exotic and tragic. . . . He took a ticket on a plane to the Colony in order to obtain background material at first hand."

COLD, YES, as many of Spark's people are, but even in this story, which is not in the first person, Spark's own balancing voice, tinged with sadness and irony, is still present. Young Daphne, filled with herself and with England, "went for walks with Uncle Pooh-bah. She had to take short steps, for he was slow. They walked on the well-laid paths to the river which Daphne always referred to as 'the Thames,' " -- and Spark adds, with great but unobtrusive sympathy for the character -- "which indeed, of course, it was."

And Spark can be very funny too. "O God, everlasting and almighty," prays a very dry and selfish woman, currently haunted by the ghost of a wronged uncle, "make me strong, and guide an lead me as to how Mrs. Thatcher would conduct herself in circumstances of this nature."

Spark writes of the places (Africa, Italy, wartime London) she knows. But what she knows best are the people . . . and, apparently, all their nasty little secrets, revealed slowly to the careful observer, and the things they may not even admit to themselves, at least until they must. In "Come Along, Marjorie," three women at a rest home discover they are all recovering from nerves. "Jennifer was delighted, 'I've got the same trouble. Fancy, all three of us. That makes us all the same.'

"'It makes us,' I said, 'more different from each other than other people are.'"

There are stories here of loneliness and the separateness of each individual in the world, and tales of thwarted love, jealousy, murder, lingering feuds, greed, ghosts both wise and wicked, demon-seed children with perfect manners, blushing girls and twisted crones. Spark reports them all with cool and precise observation that is distant enough to be absolutely unsparing, yet close enough to be both moved and moving. In the current renaissance of the short story, this collection constitutes a high point of the form, stories so wonderully subtle that their impact goes off like gunshots in the night.