BOOK REVIEW : A Dark Trip Back to the Scenes of Crime : THE COP SHOP; True Crime on the Streets of Chicago <i> by Robert Blau</i> ; Addison-Wesley; $19.95, 272 pages

The “book of death” is a loose-leaf notebook in the headquarters of the Chicago Police Department--”the Cop Shop,” as it is known among reporters on the police beat--and the coded entries reveal how the lives of various citizens of the City With Broad Shoulders came to an abrupt and bloody end.

“Fifty people had been killed with kitchen knives,” writes Robert Blau, “thirty-nine with feet, hands, or fists, one each with a necktie, a tree limb, and a hatchet, two with concrete, two with hot water, and three with lighter fluid.”

Blau’s job as a novice police reporter for the Chicago Tribune required him “to follow these acts of suffering and turn them into stories that could be served in the morning with breakfast,” he explains in “The Cop Shop”--”epitaphs with orange juice.”

Now Blau has written up his notes, fleshing out his news-page blurbs to book length, and the result is a collection of true crime stories that consciously mimics the hard-boiled prose of the mystery pulps while aspiring for both elegance and pointed social commentary.

Blau depicts an old police reporter in the haunts of the press room at police headquarters, “tumbling into the leatherette embrace of its sunken ship of a couch.” A couple of cops at the scene of a shooting “studied the constellation of nickel-sized holes curled along the car door like the Big Dipper.” And the street banter of a “gang cop” as he describes a photograph of a gang member at a funeral amounts to a kind of rap:

“That’s Hippo. He’s dead. Killed on North Avenue. Baby D. He’s doing time for murder. Fernie, sentenced to natural life for a triple murder. Rivera, he’s sells dope in the Zone.”

The author is respectful of the craft of the police reporter, who is forced to ask distrustful and sometimes distraught people a lot of intrusive questions and then face the consequences. Indeed, at its best moments, “The Cop Shop” can be approached as a kind of short course in crime reporting, and Blau’s book belongs on the reading list in any decent journalism course.

“The rules were:

“Walk to the front door slowly but confidently.

“Be firm but polite.

“Be sure there are no large dogs.”

Blau also credits the cops and firemen who were his comrades- in-arms with undeniable if slightly twisted heroism. As we are shown so vividly, they are putting their lives on the line in a battle that can never really be won: “All this for $40,000 a year,” he writes of the inner-city firefighter.

But the cops do not always come off as plaster saints. Many of them are weary, jaded, cynical; some are downright brutal. And Blau is perfectly willing to document the reality of police corruption: “Around 58 Street,” he writes, “some of the greediest people were cops.”

Nor does “The Cop Shop” paint a pretty picture of Chicago, a place where street crime sometimes appears to be a form of civil insurrection. Still, it’s somehow reassuring to be reminded that gang violence is nothing new in Chicago, even if the armaments, the jargon and the ideological stance of the gangs have changed.

“Chicago had been a gang town since the 1920s, when its tough reputation was forged by Alphonse Capone and a thousand hoods of lesser note,” he points out. “These days the gang wars were fought over drugs. And both its soldiers and its victims were the underclass.”

Blau confesses that the police beat hardened him to human savagery, and his book begins to have the same effect on the reader: “I felt emotionally prepared for ever-larger disasters,” he writes. “There was something almost pornographic about this sense of anticipation.”

And then, as if to shock us out of the complacency that he has helped to encourage in his readers, Blau gives us the heartbreaking story of a man who scalded his girlfriend’s baby in a tub of hot water when the infant would not stop crying. As the tiny victim suffered, Blau’s editor displays only a chilly (and chilling) professional interest in how the story will play in that day’s paper.

“Sounds like you got great stuff,” the editor says. “Is he dead yet?”

By the end of “The Cop Shop,” we are not surprised to learn that Blau is no longer a police reporter. Even the best of them, he seems to suggest, burn out in the end. And Blau’s account of his own brief descent into this particular hell is enough to show us why.