COULD A 26-year-old doctor with the emotional and philosophical depth of Jack Armstrong suddenly, one February night in 1970, abandon his Mickey Spillane novel, switch off the Johnny Carson monologue, and then murder his pregnant wife and two small daughters with paring knife, icepick and club? And if so, why?

When author Joe McGinniss first met Dr. Jeffrey MacDonald in June of 1979, he wasn't at all sure that the doctor had really dispatched his family that night in their home at 544 Castle Drive on the base at Fort Bragg, North Carolina. True, a jury in Raleigh, after a seven-week trial, would later find MacDonald guilty of second-degree murder in the deaths of his wife, Colette, and his 5-year-old daughter Kimberly, and guilty of murder in the first degree in the death of his younger daughter, 2-year-old Kristen. But the doctor denied it then, and from a jail cell in Texas he denies it still.

McGinniss met the doctor just before the North Carolina trial. At the time, MacDonald was living a rather sybaritic life in Huntington Beach, California, where he dwelt in a $350,000 waterfront condominium. Parked out front was a rare Citroen-Maserati with JRM-MD on its vanity license plates. Tied up out back at the dock was a 34-foot yacht, the Recovery Room.

The two men discussed McGinniss' writing a book about the doctor's ordeal. MacDonald felt abused by the judicial process and had decided that perhaps it was high time to reveal the true story. McGinniss would do the telling.

And tell it he does in almost excruciating detail. McGinniss flew back to Raleigh for the trial and lived in the Kappa Alpha fraternity house with MacDonald and his legal team. He sat through the entire trial. He talked at length with MacDonald's relatives--his mother; his odd, older brother; his sister--and the murdered wife's parents, who once were MacDonald's strongest supporters and later turned into his most implacable enemies.

McGinniss also sought out and interviewed MacDonald's medical colleagues, his Green Beret buddies, his psychiatrists, and his friends, both male and female, including those who knew MacDonald very well indeed, and those who knew him scarcely at all, sometimes for one night only.

And slowly McGinniss paints a detailed portrait of a flawed American Golden Boy: athlete, Princeton lad, medical doctor, Green Beret captain, and lover who, while still in college, married the pregnant girl he first started courting way back there in the eighth grade. Their plans were that MacDonald--once his Army tour was done--would take his residency at Yale. The family would live on a nearby farm with lots of dogs and cats and ponies. But then tragedy struck when, according to MacDonald, four drug-crazed hippies burst into his Fort Bragg home; killed his wife and children; scrawled "Pig" on the wall in blood; chanted, for some inexplicable reason, "Acid is groovy," and left Dr. MacDonald very much alive with a slight, surgically precise puncture in his lung and a few minor abrasions.

The Army didn't believe MacDonald. They wanted to try him for murder. But fortunately for the doctor, the Army so bungled its investigation that it had no choice other than to let him go free. After a burst of national publicity, MacDonald moved out to Southern California and life in its fast lane.

He worked in the emergency room of a San Diego hospital and became a popular, highly regarded member of the staff. He fell in and out of love with a series of women, each one more sensual and gorgeous than the last. He palled around with a moderately racy crowd, including some members of the Los Angeles Rams, and he seemed to have put the tragedy at Fort Bragg well behind him.

But back East there was someone who wasn't at all convinced of MacDonald's innocence. And that someone was Freddy Kassab, the stepfather of the slain wife, Colette. Kassab pored over the 153 pages of MacDonald's testimony at the Army hearing, indexing every statement, noting every inconsistency, and concluding that his son-in-law was not only a pathological liar, but also a murderer. Revenge is what Kassab wanted, even lusted for. And revenge is what he got.

In 1974, in large measure due to the ceaseless badgering of Freddy Kassab, the Justice Department reopened the case and gave it to Victor Worheide, now deceased, but then a 62-year-old trouble-shooter for the department who in the past had handled cases ranging from Axis Sally in Germany to the indictment and conviction of the former governor of Illinois, Otto Kerner.

Later that same year, MacDonald was brought before a grand jury in Raleigh, questioned by Worheide, indicted for the murder of his family, and eventually convicted. Because of appeals, MacDonald managed to remain free much of the intervening time until finally, in January 1983, the doctor began serving his three life terms in prison. The terms are to be served consecutively. With luck, he might be paroled on April 5, 1991 when he will be 47 years old.

When I started Fatal Vision I had no strong preconception as to either MacDonald's guilt or innocence. A quarter of the way through the book, due to McGinniss' skillful handling of his material, I began to suspect the doctor indeed had done it. By the end of the book I was convinced that MacDonald was guilty as hell. McGinniss himself comes to this same conclusion not reluctantly, but with a kind of sad and understandable regret. The book he has produced is really not so much written as cleverly arranged, edited, and compiled, with large chunks of MacDonald's tape-recorded and largely banal thoughts interspersed among excerpts from the trial, and the Army and grand jury hearings. In these excerpts MacDonald convicts himself.

So the question is, why did he do it? McGinniss offers evidence that it may have been because of all those amphetamines MacDonald was taking to curb his appitite. Then, too, his marriage may have turned sour, and it's suggested that when his wife came home late that night from her psychology class, there was a spat that flared into a speed-freak argument. She may have blasted him about his sexual prowess, or lack thereof, and a brawl began. Possibly, the older daughter came in to see what the commotion was and MacDonald struck her with a club. Then in a rage he killed them both with icepick and paring knife. He later could have killed his sleeping two-year- old daughter and stabbed himself out of a need for verisimilitude--for those telling details that would flesh out his tale of invading Manson- like intruders.

McGinniss reveals that MacDonald failed two lie detector tests that were arranged by his defense counsel. But this is simply more inadmissible evidence that is, at best, moot.

Fatal Vision is an absorbing and totally damning indictment of Dr. Jeffrey MacDonald. But from his jail cell the murderer still has hopes of release, exoneration, and vindication. And he also thinks Robert Redford should play him if they make the picture. The Golden Boy's dream never ends, it seems, and as McGinniss says, it is a fatal vision.