IT IS SAD AND DISCOURAGING whenever a good cop is killed in the line of duty. Sad, as are all violent deaths, whether by accident or murder, because we see not only the waste of life but the human wreckage left behind; discouraging because policemen are on the thin front line of humankind's effort to retain some semblance of civilization.

This helps to explain why the people of Riverside, California, were upset in April 1971 when two decent cops, Leonard Christiansen and Paul Teel, were shot to death when they responded to a seemingly routine burglary report. The explanation for the community's anguish had other components as well. Riverside in the early '70s was quintessentially middle American: a family town, church-oriented, peaceful -- and white. The dead policemen were white; their suspected kilers, black. Uppity black. And the killings had been accomplished through an artful ambush during a time of racial tension.

Memorials to Christiansen and Teel went up and funds for their families -- the human wreckage left behind -- flowed in. So did demands for speedy retribution. Three blacks, one of them, Gary Lawton, an outspoken civil rights activist, were arrested and charged with murder. After eight years and three trials, none of the three has been convicted of any crime.

When a good law enforcement agent dies, the idea that humans are different from animals dies its small death too. When there is added the possibility that innocent people have been charged, tried, retried and tried again on false evidence in a rush to vengeance, then sadness and discouragement are twice compounded. To this day there persists the real likelihood that this is what occurred in the case of Riverside's ambush murders.

For a long time I have held to a theory, or maybe it is only an opinion, about the law, lawyers and judges, and their ability to get at facts fairly. It is that the purposes and the actual workings, and the defects, of our legal truth-determining procedures can best be demonstrated not, on the one hand, in all-encompassing treatises, which are almost inevitably too broad and too thin, nor yet in the comic book approach of such cinematic claptrap as the current And Justice for All , but rather in knowledgeable and close dissections of particular litigated cases. That is why Anthony Lewis' study of Earl Gideon's case, Gideon's Trumpet and, I hope, my own study with John Kaplan of The Trial of Jack Ruby have been at least as useful as many books with more promissory titles. And that is why Ben Bradlee Jr.'s meticulous tracking of the Christiansen-Teel murders is a welcome, if flawed, effort.

I suppose it should come as no surprise that a young fellow with this author's family name should turn out to be a better than average investigative reporter. Bradlee, who is 30 years old, began his coverage of the ambush murders as a reporter for the Riverside Press-Enterprise but resigned from the paper in 1975, when the case ended, to dig more deeply into it. His book is not a rehash of his newspaper accounts, detailed as they were. Bradlee spent six more months conducting over 150 interviews with nearly everyone involved in the case; the only ones he missed were the few who would not talk with him. He picked his way through 25,000 pages of court transcript, read hundreds of police reports and listened to miles of taped interrogations. The Ambush Murders is a fact-mountain. Bradlee describes the crimes, the frantic and often inept police investigation of them and the three trials of the accused, all in the most minute detail.

The scenario and the cast are disturbingly familiar: There are the young police investigators maddened by their fellows' fate into the use of questionable investigative tactics; the timid souls unwilling to get "involved," even when faced with the possible sacrifice of guiltless men's lives; bumbling judges; prosecution and defense lawyers with limited talents and questionable motives; perjurious witnesses; closet racists, and proponents of dubious crime-solving gimmicks, most notably the ubiquitous "voiceprint." Towering above the other participants is the furiously obstreperous principal defendant, Lawton, who reminds one of Chicago Seven defendant Bobby Seale. Lawton, who frequently had to be ejected from the courtroom, had an epithet for almost everyone. The prosecution's key witness, a singularly obtuse policeman named Ronald Lund, was a "racist assed punk." The prosecutor himself was a "lying ass", the judge, a "lousy racist hypocrite." Others were "grapeheads." But after he was at last acquitted by a Middle American jury, Lawton's words were simply "Ladies and gentlemen, thank you. Thank you." He had lost four years of his life. One juror, after his second trial, had said, "the murderers are still at large and they've got the wrong men."

Bradlee's book has two shortcomings. There is a tendency to sink into breathless journalese. ("Thus began this lamb's journey to the slaughterhouse" is a '20s sob-sister way of referring to a bruising cross-examination.) And the author puts too little of himself into his accumulation of facts. Whether that disgruntled juror was right or wrong is left in large measure to the reader to determine. Bradlee expresses no firm opinion of his own. His book ends with the unelaborated statement that "the ambush murders case was closed." Because he is so obviously an adept assembler of facts, Bradlee's failure to provide an overlay of analysis and conclusion is more than vaguely disappointing. There is as much to his book as meets the eye, but no more.