MARGARET TRUMAN as a mystery writer recalls Dr. Johnson's comparison of a woman preaching to a dog walking on his hind legs: It may not be done well; the wonder is to find it done at all.

And the truth is that it is not done that badly either. Murder on Capitol Hill (Arbor House, $11.95), Truman's second mystery novel, is a cut above the first, Murder in the White House , in which she killed off the secretary of state. This time it's the Senate majority leader. Truman does not scrimp on her murder victims.

Truman's prose style (if there is a ghostwriter, as rumors have hinted, he should be fired) is about as inspired as a bureaucratic press release. She clutters her plot and cast of characters.

But the former president's daughter writes entertainingly about the Washington scene and not without a touch of gentle amusement. She has been to these receptions with the shrimp trees, meat-filled pastry nibbles and centerpiece of ice sculpture. She has gone behind the closed doors of the White House and Capitol Hill. She has met the lobbyists, the political hangers-on, the art patrons with their precious projects, the persistent reporters, the freebee scavengers, the Washington hostesses.

In Murder on Capitol Hill , Cale Caldwell, the wily Senate majority leader, is stabbed to death at a Hill reception in his honor. (The ice pick had been left behind by the caterer's sculptor, whose inspired creation was an ice sculpture of Caldwell's home state of Virginia.)

Lawyer Lydia James, a refreshingly self-assured, sophisticated, 40-year-old heroine who is not too old to jog three laps around the Reflecting Pool, is asked by the widow to serve as counsel for a congressional committee investigating the murder. It would be quibbling to question whether such an inquiry would be within the purview of a congressional investigation.

Lydia, a friend of the family, already knows most of the prime suspects: Mark, the senator's son who has joined a fanatical religious cult to his father's dismay; Quentin Hughes, an abrasive talk-show host; Jason DeFlaunce, an artful fund-raiser for cultural projects; Sen. Wilfred MacLoon, a bitter political adversary of Calwell; Cale, Jr., the son whose success as a lobbyist depends on his family connections. Not even Veronica Calwell, the grieving widow, is above suspicion. She seems surprisingly reconciled to having her son, Mark, take the blame.

The senator's murder dredges up memories of an unsolved crime a few years earlier. Jimmye, the Caldwell's adopted niece who was carving out a career as an aggressive TV reporter, had been bludgeoned to death in a Washington park. Had she left behind a tape surreptitiously filmed at the camp of Mark's religious cult?

It takes a long time for Truman to sort out these complicated entanglements. She never manages to pull the dangling ends together into a tidy package. Except for Lydia, the characters are stock figures from central casting. But, particularly for Washington readers, there is that moment of recognition when Truman describes the hors d'oeuvres on the table, cocktails at the Madison bar, the view from the bridges over the potomac, and the diplomats, lobbyists, FCC lawyers, congressmen, lobbyists, and hostesses in the nation's Capital.

Sweet & Deadly (Houghton Mifflin, $8.95) introduces a newcomer to the mystery field. Charlaine Harris makes her debut with a first-rate mystery with special character: a small-town Mississippi Delta setting, a plucky, bright heroine, a tight plot that plays fair with clues for the reader, and motivation as convincing as it is surprising in the final revelation.

Catherine Linton has come back to her hometown of Lowfield after the death of her mother and father in a suspicious automobile accident. She is convinced that her parents were murdered, although she cannot divine what motive the killer could have had. Her grief is combined with a promise to herself to find the murderer.

In spare hours from her job as society editor of the Lowfield Gazette , she practices target shooting at an abandoned shack on her grandfather's land. It is there that she stumbles on the body of the nurse who worked with her doctor-father. Then comes a second murder when the reporter-tenant of the small garden house that had served as Dr. Linton's office is bludgeoned to death.

Catherine comes to know her neighbors and friends -- and herself -- much better before she uncovers the reason for the murders in a chance newspaper column and the memory of an old black woman who served as a maid in the Linton household.

The small Southern town of Lowfield springs to life on the page of Harris' novel. You feel the drugging heat, the sting of horseflies, the jarring bounce of the baked and rutted roads through cotton fields. In this small, self-contained world, everyone seems to know everything about the neighbors. but there are secrets under the surface of small-town friendliness, and one provides the motive for murder.

Harris, who grew up in the Mississippi Delta region, also reflects a time of social change in Catherine's relations with the black people of her Southern hometown. When a black librarian offers refuge in her cramped crackerbox of a house, Catherine knows that here would-be benefactor is risking a shocked refusal from a white woman. The young black deputy who takes Catherine's statement at police headquarters is the son of the family's old maid, known only as "Betty" without a last name. After a year away at college, Catherine had decided this was "a shameful thing." But she still finds herself "less comfortable with blacks in her own town than she was with blacks anywhere else . . . the old attitudes caught at her and strangled her attempts to be easy in an uneasy situation."

In Sweet & Deadly , Harris offers more than a well-plotted mystery.

Killing No Murder (Scribner's, $8.95), a mystery-suspense novel by Howard Shaw, takes its intriguing title from a 17th-century pamphlet that argued Oliver Cromwell should die for the good of the country. At Claydon Court, an English boarding school for boys, there were those who suggested that Headmaster Henry Carter should go for the good of the school. But only one of these felt that Carter should take his leave by being stabbed and thrown into the school swimming pool.

Shaw, who teaches at Harrow, knows the milieu of the English public school, that much-maligned institution in autobiographical novels of British writers. Detective Inspector Barnaby of Scotland Yard discovers all is not quite proper at Claydon Court School. There are academic rivalries, bruised egos, love escapades in the grass, voyeurism, and war-related psychoses.

The scenes with the boys and schoolmasters are often lively and amusing. Unfortunately, Shaw needs a refresher course in the rudiments of mystery plotting. The solution is contrived and the motivation is weak.

"You have to wonder what else is going on under the surface in our peaceful village."

By the time this observation is made, the heroine of Erica Quest's Design for Murder (Doubleday Crime Club, $9.95) has settled comfortably within the arms of her true love, having survived a face-to-face encounter with a murderer and innumerable agonizing moments.

Quest doesn't miss a cliche in this predictable mystery of romance and suspense. Tracy Yorke, her heroine, blithely stumbles over clues and revelations after finding the bludgeoned body of her employer, who was a talented interior designer and enterprising womanizer.

The quiet village of Steeples Waslop turns out to be an English Peyton Place with discarded mistresses, juggled estate accounts, and secret bigamies. Not even Tracy, a quite likable heroine, can redeem this romantic suspense tale written by rote.