MICHAEL GILBERT, a smooth storyteller with a touch of graceful wit, has added a devilish Christie-style twist for a shocker in his latest mystery, The Killing of Katie Steelstock (Harper & Row, $10.95).

The small English village of West Hannington boasted one celebrity, Katie Steelstock, a young singer and television personality known as "our Katie" to millions of viewers. So when Katie's body is found beside the boathouse after a village dance, it is a murder of some consequence and becomes a media event. An ambitious, tough Scotland Yard superintendent wants to clear the case quickly as a step to promotion and latches onto the obvious suspect. He is Jonathan Limbery, a young newspaper editor of unruly temper and radical views, who once had been Katie's lover.

But there is also the London connection, where it seems "our Katie" hadn't been exactly the village lass. Her way to stardom had been paved by cold ambition and a willingness to use people, including a porno photographer. Gilbert, the author of espionage novels as well as mysteries, is a stylish writer to be respected even when his performances are flawed. This time he is on the mark. He deftly handles his layered plot with its interweaving stories and characters: The police, with their own rivalries, including the ambitious Scotland Yard man and Sgt. Ian McCourt, a young local detective with a stern Scottish Presbyterian conscience, who doggedly pursues his own investigation; the villagers, with their own secrets, including Jonathan, the village squire, and a local schoolboy; the Londoners, with their orgies and dirty pictures.

At the end, there is a stunning surprise. The way has been prepared with psychological hints, but the question is whether Gilbert has been scrupulously fair. Each reader will have to decide for himself at the end of The Killing of Katie Steelstock.

The Slasher (Dodd, Mead, $7.95) takes Dan Fortune, the New York private eye, to the West Coast, the home turf of Sam Spade, Philip Marlowe and Lew Archer. Michael Collins, whose one-armed private investigator has handled nine earlier cases, carries on the Hammett-Chandler-Macdonald tradition with skill and finesse.

Fortune is a loner, slightly world-weary, yet a man with his own code of honor and sense of jutice. An old flame, Marty, asks his help when the niece of her new husband disappears. The girl later is found murdered in a fashion that leads police to believe that she is another victim of a pyschotic slasher.

But Fortune doesn't accept the police version. His investigation takes him to television game shows, fashion shows, and elegant Malibu beach parties. There he finds people with dark secrets in their past, and, as in Ross Macdonald, the motive for murder lies a-mouldering in the psyche.

Hard-boiled detectives, who meet people at their worst, are philosophers of human nature. Fortune is no exception. In the end, as neighbors jeer police making an arrest, Fortune, echoing Hannah Arendt's sudy of Eichmann's trial for Nazi atrocities, observes: "The worst danger isn't the Hitlers and the Himmlers, the Eichmanns and Mengeles . . . The danger is the ordinary man with his wife and children, his pleasant house, his friendly community. . . . We know we have monsters among us, but they can't go far without those who serve them and those who join them."

The let-down that comes at the end of Michael Underwood's A Clear Case of Suicide (St. Martin's, $8.95) is all the more disappointing because things have been going so well until then.

We do wonder why Laurence Deegan, a prosperous 50-year-old lawyer and candidate for a judgeship, should slash his wrists in his chambers. His family life doesn't seem strained, with a supportive wife and two sons having reasonable success. Why would he commit suicide?

Richard, the younger, adopted son, who is a policeman, is obsessed with the question. On his own, he checks two legal cases in which his father was involved -- a murder charge against a powerful millonaire's son and the theft of secret documents. Tension builds as Richard follows leads to his father's past. The, plop, Underwood brushes off the denouement in a few pages as if we really should not have cared.

June Thomason's Inspector Rudd, an avuncular, pink-cheeked policeman who chats up witnesses, is called in on another rural village murder in Alibi in Time (Doubleday, $8.95).

What Thomson adds to the conventional English mystery is psychological insight. It extends to Rudd as well as her victims, murderers and involved villagers. Rudd can understand a father's relationship with his daughter because "everyone of his own relations have been limited by the same reserve" with private emotions.

Thomson skillfully establishes her characters in shifting scenes at the beginning -- Lewis Shand, the schoolmaster; his daughter, Hilary, who seeks joyless sex after being jilted; Kitty Fulton, a widow, who rents her gatehouse to Patrick Vaughn, a bearded, amoral writer, who uses blackmail to gain power over people. Rudd doesn't believe Vaughn was killed by a hit-run driver and proves it with solid legwork. Thomson is an observant, intelligent writer for readers who don't chafe at the slow pace of English mystery.

A positive delight awaits readers who have not encountered Sgt. Beef, whose lower-middle manners and speech are the despair of Townsend, who carries on his Watson-like role of narrator-collaborator with condescending superiority toward his colleague's common-sense detection.

Leo Bruce, who also writes the Carolus Deene stories with a schoolmaster-historian as sleuth, is the mystery pseudonym for Rupert Croft-Cooke, British novelist, biographer and antiquarian bookseller. Sgt. Beef first appeared in the 1930s. Now Academy Chicago Ltd. is publishing five of the Sgt. Beef adventurers ($7.95, each).

They include Cold Blood, in which the murder weapon may be a croquet mallet, and Case for Three Detectives, a spoof on the methods of three famous fictional sleuths (Lord Peter Wimsey, Father Brown, and Hercule Poirot), with Sgt. Beef proving them all to be wrong. The other three are Case With Ropes & rings, Case for Sergeant Beef, and Neck and Neck.

And for summertime reading, there is a bounty of recent paperback reissues of mysteries, ranging from classics to good entertainers.

Harper & Row's Perennial Library ($1.95) offers Edmund Crispin's satiric Buried for Pleasure, with Gervase Fen, the capricious Oxford Fen standing for Parliament while playing amateur sleuth; Cyril Hare's Untimely Death, and Francis Illes' Malice Aforethought, the 1931 story of "a commonplace crime" with its classic opener: "It was not until several weeks after he had decided to murder his wife that Dr. Bickleigh took any active steps in the matter."

For fans of the very proper British mystery, Bantan Books ($1.95) has revived earlier novels of Catherine Aird and Patricia Wentworth. Aird is at her best in The Stately Home Murder, neatly balancing witty observation with detection. In The Religious Body, murder takes to the nunery. Wentworth's Maude Silver, the spinster who conducts private enquiries, appears in The Listening Eye and The Fingerprint.

The Peter Duluth mysteries of the mid-1930s and '40s are being reissued by Avon ($2.25). All the stories carry "puzzle" in their titles -- Puzzle for Fools, Puzzle for Wantons etc. Unlike such gay-hearted couples as Nick and Nora Charles, the Duluths have their problems. Peter, a theatrical producer, met his actress-wife in a hospital while he was taking a cure for alcoholism and Iris was being treated for depression. In the earlier mysteries, their psychiatrist joins them.