From reading Margaret Truman, one would gather that the cleaning people in Washington spend much of their time washing blood from the floors of our most noted public buildings. First there was "Murder in the White House" (a building in which she knew all the nooks and crannies better than most), then "Murder on Capitol Hill," "Murder in the Supreme Court"--and now "Murder in the Smithsonian."

And a fun murder it is.

Imagine a black-tie party at the National Museum of American History in honor of the opening of a new exhibit, the guests including the Vice President and his wife. As guests, drinks in hand, mill about the Foucault pendulum, making small wagers on how long it will take before the pendulum strikes down the next red marker, drops of blood fall onto the compass rose from the floor above. When Vice President William Oxenhauer looks up, the body of his good friend, Dr. Lewis Tunney, the night's keynote speaker, topples over the railing, Thomas Jefferson's sword sticking in his back. Enough to make you eschew your claret.

Truman's cast of characters includes art dealers, scholars, collectors, patrons and curators. Along the way people get shot, mugged (in the courtyard between the wings of the National Gallery of Art), stabbed frontally and bashed in the head. It's a naughty world these people of the arts inhabit.

And while these acts of violence are taking place, the Smithsonian also is receiving threatening notes from an anonymous writer who claims to be a descendant of James Smithson, the illegitimate son of the Duke of Northumberland who in 1829 bequeathed his fortune to fund the scholarly society that administers the museums. The note writer, who eventually follows through on his bomb threats, demands that the assets of the museums be turned over to him as the rightful heir of Smithson.

But it is art theft and forgery, rather than a mad bomber, that is at the heart of this tale.

Truman's heroine is Heather McBean, a Scotswoman who was engaged to the late Dr. Tunney. The diligent cop is Capt. Mac Hanrahan, the Metropolitan Police Department's chief of detectives, whose talents include gourmet cooking. Mac, recently divorced, has eyes for Heather. He also has eyes for the possible murder suspects: Congressman Jubel Watson; Alfred Throckly, the director of the National Museum of American History; Chloe Prentwhistle, a museum executive; Walter Jones, Prentwhistle's secret husband, who is a consultant to the Smithsonian; Ford Saunders, Prentwhistle's assistant, who has a penchant for dressing in drag; and Dr. Evelyn Killinworth, a shadowy 300-pound art professor and lecturer who had been a friend of Heather McBean's late uncle Calum, the donator of the Harsa medal.

It was knowledge of the theft of the Harsa medal, the gem-studded emblem of the Legion of Harsa--the organization started by Jefferson in opposition to the elitist and secret Society of the Cincinnati, whose first president was George Washington--that led to the murder of Dr. Tunney. And it is the Harsa medal that makes every step dangerous for Heather McBean throughout Washington, London and Edinburgh.

Truman is adept at taking us into the museum world, like a Thomas Hoving explaining the politics and devious machinations of art collecting. And for readers who like to go sightseeing without leaving their beach chair or recliner, Truman's wanderings through the First Ladies exhibit in the Museum of American History, the Venetian and Florentine sections of the National Gallery, a squalid part of London and a castle near Edinburgh are vivid and informative. Her characters, real enough in Washington, but perhaps hardly recognizable elsewhere, are interesting and believable.

Most important, "Murder in the Smithsonian" is a good, light read--it probably is not coincidental that the publication comes just in time for the beach and swimming pool trade.

But Truman can be a careless writer. At one point, Heather McBean and Mac Hanrahan are conversing by phone. In the middle of the conversation: "She looked up at him, smiled quickly." By phone?

I mention this incident because Truman has a more serious lapse in recalling what she has written at a more crucial point in her story. In the obligatory closing chapter that ties up loose ends in nearly all mystery novels, Truman leaves one loose end pointedly untied. Because it is crucial to the attribution of guilt, all I will say is that it relates to the killing of an Arab dealer in London. But it jarred me nearly as much as when Leon Uris, in "Trinity," needlessly killed off his narrator several pages before the finish, leaving one to wonder who in blazes was left to conclude the story.

More careful editing could have caught these inconsistencies. I suspect Truman's novels of Washington will continue to entertain both mystery and Washington buffs. Even now, Give-'em-Hell Harry's daughter likely is zooming in on her next historical site. Will it be "Murder at the Eternal Flame?" "Murder at Kennedy Center?" Maybe a period piece, "Murder at Ford's Theater?" There's this president of the United States, who has just beaten back an army of rebels, out for a night's relaxation. Enter this disgruntled actor . . .