NEAR THE END of Murder in the CIA (Random House, $17.95), Collette Cahill, the heroine of Margaret Truman's latest novel, admits that she is "terribly mixed up and disillusioned." The reader will share that feeling.

This time Truman, who has proved herself to be a competent professional writer of mysteries, has plunged into the world of international espionage. The plot, as devious as a CIA undercover operation, is full of disinformation to confuse the reader. Cahill's colleagues in the Pickle Factory are stock figures for anti-CIA novels -- evil men with the "same morality, same ethics, same game" as their adversaries.

Truman has a special purpose in writing Murder in the CIA. President Truman presided over the agency's creation. He had serious doubts about setting up a national intelligence organization, fearing the excesses of a runaway government arm with no accountability. Recent revelations have shown how well-founded his doubts were. Truman makes her statement powerfully and persuasively.

What she does not do as well is write a well-structured espionage thriller with believable characters and events.

It all begins when Truman bravely kills off a literary agent. Barrie Mayer, who also is a part-time courier for the CIA, is waiting in line at London's Heathrow Airport to board a plane for Hungary when an assailant explodes a vial of prussic acid in her face and snatches a locked briefcase.

Cahill, who has been working on a CIA assignment at the American Embassy in Budapest, is picked to investigate her best friend's death. Her bosses fear a leak in a Bay-of-Pigs-like operation to foment an uprising in Hungary.

Cahill, who is incredibly naive for a trained CIA operative, becomes disillusioned when she turns up CIA dirty tricks. She doesn't know whom she can trust and who might be a double agent.

Even in a morass of plot convolutions, Truman can write strong scenes. She has done her research on the CIA. She writes as if she has had a grand tour of the Langley headquarters and a briefing on tradecraft.

Murder in the CIA, the eighth in Truman's Washington-based series, leaves the reader as mixed up as her heroine, trying to sort out a tangled plot with too many shifting scenes and flip-flops from a heroine who is as uncertain of her villain as her true love.

Grisly Death

WHEN Fadeout, the first of the Dave Brandstetter mysteries appeared in 1970, Joseph Hansen was courageously breaking new ground with his non-apologetic portrayal of a homosexual private eye who was shrewd, competent and tough-minded. Brandstetter's sexual orientation was handled without sensationalism. He was having problems with lovers, but, then, most private eyes do.

Now comes Early Graves (Mysterious Press, $15.95), the ninth in the Brandstetter series. Inevitably, it deals with AIDS. A serial killer has been stalking AIDS patients and knifing them to death. When Brandstetter comes home to find a corpse on his doorstep, police believe that Drew Dodge, the dead man, is the sixth stabbing victim of the AIDS-obsessed killer.

Tracing the homosexual liaisons of the first five victims, Brandstetter, who has always sought monogamous relationships himself, finds the dead men had promiscuous sex lives that spread AIDS and resulted in grim statistics.

Unfortunately, Hansen is not at his top form in Early Graves. Halfway through the book, the psycho serial killer conveniently confesses to the first five murders. That leaves Brandstetter to solve the murder of Dodge, who turns out to be a yuppie real estate developer who was a bisexual with a wife and children. That solution is contrived with overworked Freudian overtones.

In his most recent books, Hansen has seemed to grow weary along with Brandstetter, now in his sixties. His plots have been weak, and he has slipped into soap-opera sentimentality in chronicling Brandstetter's most recent affair, with Cecil, a 25-year-old TV newsman.

Costume Drama

IT'S Halloween night in the 87th Precinct, and Ed McBain offers more tricks than treats in his latest police procedural. In Tricks (Arbor House, $16.95), McBain follows the members of the 87th squad on one shift of duty as they handle several cases: (1) the real-life disappearing act of a professional magician (2) the murder of liquor store owners by what at first appears to be a band of four costumed children (3) discovery of parts of a dismembered body (4) a slasher who is killing hookers. Each of the mini-plots had its own kind of "tricks."

The 87th Precinct novels -- this is the 39th one -- make up what well may be the best police procedual series written. They deserve their popularity on best-seller lists. McBain is a master storyteller. His dialogue crackles. The twisty, ingenious plots have socko surprises.

Yet some recent outings have been less than inspired, and Tricks is another sub-par entry. Lately McBain has seemed content to use the police-blotter approach of Dell Shannon.

Leaping Lizards!

WHAT A joy to make the acquaintance of Jimmy Flannery, a sewer inspector and precinct captain in Chicago's 27th Ward. Thanks be to Robert Campbell for this original character -- a kind of political ombudsman who takes care of neighbors -- and his wacky adventures.

Flannery makes his hardcover debut in Hip-Deep in Alligators (New American Library, $16.95). His earlier outings (The Edgar Award-winning Junkyard Dog and The 600-Pound Gorilla) were paperback originals.

As Flannery tells the story in his big-city street argot, he's been sent back to the sewers as a lesson for crossing his ward boss. He's wading through the muck and slime when he finds a body that has been chewed in half -- "a hell of a way to start a week."

As ward captain, Flannery also has other problems. Pigeons have been disappearing from roof-top lofts, and one owner, a Haitian immigrant, is being harassed by health inspectors for keeping her flock in her bathroom. A pigeon feather has been found on the severed corpse, and a woman zoologist confirms Flannery's nightmare fear: The body has been chewed in half by a huge tropical reptile (What happens to all the pet baby alligators flushed down the toilet? Flannery has mused on his sewer rounds).

But the killer was not a grown-up pet alligator, Flannery is to discover when he flushes out a bizarre drug-smuggling scheme.

Flannery is a charmer with his big heart and political smarts. He is surrounded by oddball characters viewed with affection and tenderness by Campbell. In the midst of some rather goofy goings-on, he manages to keep the plot moving at a smart pace.

Fun in the Sun

FRED CARVER, the Florida private eye with a limp from a shattered kneecap suffered when he was a cop, makes his second appearance in Scorcher (Holt, $16.95). John Lutz, a writer with uneven talent, doesn't succeed in igniting enough suspense to match the title.

Scorcher opens with punch and promise. It ends with a mishmash of melodramatic revelations of family secrets from the past. They are quite unbelievable.

When an old buddy from the Orlando police homicide squad comes to visit, Carver senses something is wrong: His 8-year-old son has been torched to death by a serial killer who uses a homemade flame-thrower fashioned from a scuba tank.

For Carver the only justice is revenge. When evidence points to a schizophrenic young man from a wealthy family, Carver agrees to a police ruse and is hired by the family to find their son before trigger-happy cops do. He has an unofficial license to kill. By the time he tracks down the schizophrenic young man, Carver is having doubts about his guilt and begins to suspect that someone may have set up the 20-year-old to take the blame.

Jean M. White reviews mysteries for Book World on the third Sunday of the month.