BETWEEN 1971 and 1977 Detective Bob Leuci was the centerpiece of a sprawling federal undercover probe into the corruption in New York City law enforcement. Leuci had belonged to an elite city-wide narcotics squad (the special investigations unit, or SIU) that was later torn to pieces by indictments and resignations. He could speak with authority on the subjects of malfeasance, misfeasance, and nonfeasance. He could tell prosecutors just which cop, lawyer or bail bondsman was not above taking a bribe, and then, with a listening device wrapped uncomfortably around his waist, he could also prove the accuracy of his assessments by delivering the bribe money himself.

Leuci had an influence, for good or ill on a lot of lives during his undercover years. Shady characters who made the mistake of doing business with him wound up unemployed, disgraced, imprisoned, and in two cases, dead. On the other side of the law -- the right side -- a number of federal prosecutors who worked on the Leuci investigation, substantially advanced their careers as a result. (Richard Ben Veniste went on to become deputy Watergate special prosecutor. Nicholas Scopetta became New York City's Commissioner of Investigation, and is now on the faculty of New York University.)

Leuci had some close calls. He was repeatedly frisked, challenged or threatened by bad guys inside and outside the police department once they had begun to smell a rat. Prosecutors gave him a hard time, too, when they caught him in some fairly large lies about corrupt acts in his own past. The possibility surfaced that Leuci himself would be the final casualty of the Leuci investigation.

But the currents eventually wafted him to safety. Prince of the City, Robert Daley's retelling of Leuci's story, is now a Book-of-the-Month Club selection. The movie rights went for a reported $500,000, and John Travolta has been approached about the starring role.

Joe Nunziata was Leuci's friend and fellow detective in the late '60s. Caught on the receiving end of a bribe and given the choice of being prosecuted or "turned" into another anti-corruption undercover operative, Nunziata found a third option. He killed himself -- shot himself in the heart with his service revolver -- on the day of a scheduled confrontation with federal prosecutors and officials of the Bureau of Narcotics and Dangerous Drugs (now known as the Drug Enforcement Administration).

Point Blank is a fictionalized treatment of Nunziata's story, for which he has been renamed "Joe Longo." It is a book with many villains, and the worst villain of all is a narcotics detective named "Gil Lacey" who bears a powerful resemblance to Bob Leuci.

In their preface, the authors of Point Blank affirm the truthfulness of their story but add that they have changed most of the names for "obvious reasons." The reasons, apparently were not so obvious to Daley, who chose to use real names in dealing with many of the same people and events. Daley has in effect dared anyone who challenges the accuracy of his account to sue.

Although there are factual discrepancies between the two books, the bigger difference is one of perspective. Daley seems to begin with the assumption that crookedness among cops and lawyers was, in New York City in the '60s and early '70s, a desperate problem demanding desperate measures. Grosso and Rosenberg appear more upset by the measures than by the problem. They portray "Joe Longo," as (in the words on the book jacket) "a devoted father and dedicated cop who was driven to his death by callous manipulators."

Both books agree that "Longo"/Nunziata was a purely accidental victim of an investigation that had been after bigger fry. And they agree that he repeatedly refused a B.N.D.D. undercover agent's bribes -- although he did nothing to report the offers -- before finally succumbing.

So Grosso, an ex-narcotics detective himself and a principal figure in the book and movie The French Connection, may have cause for believing that his friend Nunziata was very badly treated. Point Blank reminds us again that ambitious prosecutors perhaps above all other public servants with real power, bear watching.

Which is more or less what "Longo" had to say in his suicide note. After declaring his love for his family and his insistence that "nothing that was done, was done with criminal intent," he concluded the note with a prayer: "May God look down and show, in his own way, the wrong, unjust and malpracticed deed that has been done by B.N.D.D. and their people."

"Longo"/Nunziata's suicide and the events that led to it occurred when New York City cops were being investigated from a dozen different directions at once. But Nunziata, among many others, went right on doing business as usual. This makes him an odd hero to say the least. And it conveys, vividly, just how routine corruption had become, just how strong an influence was the peer pressure of corrupt cops.

Leuci, also, makes an odd hero. What drove him to be a corruption-fighter -- what blend of conscience, fear and vanity -- is never fully explained in Prince of the City. Perhaps Daley hasn't quite figured it out himself. The prosecutors who took Leuci's corruption cases to court often wondered if their star witness had come completely clean with them. Readers of Prince of the City may wonder, too, despite the book's clipped, colloquial style that seems to promise total candor.

A whole raft of writers has tried to capture, in fiction or nonfiction, just what befell the New York City cops during the time of the Knapp Commission. The remainder shelves are littered with such volumes as Peter Maas' Serpico, and William Phillips' Rogue Cop; perhaps the two best books of the lot -- because they tell powerful stories that touch only incidentally on the problem of corruption -- are James Mills' Report to the Commissioner, and David Durk and Ira Silverman's The Pleasant Avenue Connection. After Prince of the City and Point Blank, the need for further entries in the field, it seems to me, is not pressing.