THE ASSASSIN was the American, Michael Townley, high school dropout, gifted bomb maker, and son of a Ford Motor Company executive. The victim was the Chilean, Orlando Letelier, diplomat, intellectual, lover and poet--blown away September 21, 1976 on Massachusetts Avenue by a car bomb of Townley's design and manufacture.

Taylor Branch and Eugene M. Propper have written a detailed, fascinating and revealing account of how the U.S. bureaucracy with what seems to be almost equal amounts of bumbling, doggedness and guile finally managed to crack the case and put at least Townley behind bars while watching helplessly as the courts freed two other suspects because of what one of the federal prosecutors branded as "Rube Goldberg logic."

There are at least 76 major principals in this lengthy, twisting, absorbing narrative of international intrigue, treachery, and political chicanery that spans three continents. It is a tale that should satiate, at least temporarily, even the most insatiable conspiracy addict, for it was indeed a conspiracy with all the conspiratorial elements of loose ends, slender reeds, red herrings, and witting and unwitting assets.

Propper himself was the young federal prosecutor who headed the government's investigation. Allied with him-- or sometimes against him--was the venerable FBI, bogged down in its own internal war between what the authors happily choose to call the Palm Tree Peekers and the Door Kickers, a classification that I trust will stand for some time to come. The FBI Door Kickers, of course, were of the "let's go arrest somebody" school, while the Palm Tree Peekers were more of the "but what if it's the wrong guy" persuasion.

The authors' brisk, zip-along style curiously suits their grim, funny, macabre account of murder, terror, betrayal and bungling. Their characterization is usually excellent, for they have managed to pry behind the public and private masks to reveal the principal characters for what they are--all too human humans with all too human faults, strengths, foibles, fears and ambitions.

If their portrayal of the FBI is accurate, then we must needs fear and tremble for the Republic and wonder whether Epfrem Zimbalist Jr. wasn't really lying to us all those years on television. For the FBI seems to have ossified itself into a bone-rigid bureaucracy ruled by its Drones. Fortunately, there remain quite a few free spirits among its agents both here and abroad, and it was their dogged efforts that contributed substantially to the solving of the Letelier murder.

Still, the case had its Keystone Cops aspect. Acting on a tip that a female terrorist was flying into New York from Europe, a covey of FBI agents tore after her on a mad chase that led from New York to Michigan to Canada and down to Florida, whereupon the agents put the arm on her only to learn that she was really a wealthy, jet-setting friend of Ted Turner, the sports and TV magnate.

In this tale studded with bizarre characters, few stand out more vividly than does Mariana Callejas. For it is she who married Michael Townley, 10 years her junior, and it is she who joined him in Europe for an assassination attempt that went sour.

Townley was Callejas's third husband. As a teenager she fled Chile, went to New York, converted to Zionism, left her Catholic husband of three months, and journeyed to Israel to live in a kibbutz. Years later, back in Chile, she married Townley. The Chilean intelligence agency, DINA, hired them both some time thereafter.

Meanwhile, Callejas had become a gifted short story writer. She whiled away her time on the plane to Europe where she would join Townley in the abortive assassination attempt by plotting a story about an elderly Swiss gentleman she had met on the plane. I have the feeling that Callejas' strange life might offer more than a few short stories.

Branch and Propper do an excellent job of detailing the diplomatic and legalistic backing and filling that finally led to Townley's extradition from Chile. They do an equally good job of explaining Townley and why he would turn from selling Collier's Encyclopedia and Bernie Cornfeld's mutual funds to the assassination business.

Perhaps if one particular customer had only paid for his encyclopedias, Letelier might still be alive. For in 1962, according to the authors, Townley "finds himself in a nasty dispute with a future President of Chile, Eduardo Frei, who, as Townley sees it, grandly offers to buy a set of encyclopedias but then changes his mind and refuses to pay for it when Townley delivers the order. In later years, Townley will recall the incident as a fitting introduction to Frei and most other Christian Democrats, whom he will regard as vacillating, irresponsible politicians."

It may be that out of such small slights are injustices collected and assassins made.

Then there are the Cubans. For it is this certain small embittered band of ruthless exiles, bound together by their hatred of Castro, who enabled Townley to carry out his assassination scheme.

"We want you to put the bomb on, my friend," one of the Cubans tells Townley. "Our movement wants the hand of Chile very close to this act. You put it on. We will set if off. That seems like a fair partnership to us."

So Michael Townley, the former AAMCO mechanic, fashioned his bomb out of TNT and some cake tins he bought from Sears, and placed them under the car that would explode and kill Orlando Letelier and his innocent bystander, friend and aide, Ronni Moffitt.

There was an extra cake tin left over and Townley took it back to Santiago with him for his wife to use in the kitchen. For, as Branch and Propper note, Michael Townley was never one to waste anything.