Henry Hill, wherever he is, is not happy. All he ever wanted to be was a "wiseguy," a mobster. He was. But now he is a middle-class businessman with a $150,000 neocolonial home and a Keogh plan. He is, in a word (his word), a "schnook."

Hill was 13 when he became an apprentice gangster. When he got some money, he bought a dark-blue, pin-striped suit with wide lapels. His mother screamed, "You look just like a gangster!" Hill was pleased. The story of this man's decline into his current status, which is something like respectability, is told in Nicholas Pileggi's fascinating "Wiseguy: Life in a Mafia Family."

Hill was to the mob what a utility infielder is to a baseball team -- useful and busy. But on May 20, 1980, he found himself in a cul de sac and decided to cease to exist.

He was in jail, facing a life sentence for narcotics trafficking. Prosecutors were investigating his role in the $6 million Lufthansa robbery at Kennedy Airport (the largest successful cash robbery in U.S. history) and the 10 murders that followed. Investigators also were interested in the body in the refrigerator truck, a body that took two days to defrost before there could be an autopsy. There also were the Boston College basketball players he had bribed for point shaving and, oh, yes (organized crime has its own synergism), the automatic weapons and claymore mines stolen from a Connecticut armory.

Forced to choose between a long prison sentence and betrayal of his friends, Hill opted for betrayal. He became one of 4,400 persons in the Federal Witness Protection Program and began testifying. It was just another transaction, another improvisation by a hustler who had reached middle age without ever having voted or paid taxes or having had a legitimate Social Security card or driver's license.

The mob's biggest bonanza was the opening of Kennedy Airport. It is the size of Manhattan from the Battery to Times Square and employs 50,000 people, some of whom feed tips about cargo to wiseguys. The Lufthansa tip came from a $15,000-a-year cargo supervisor with an estranged wife, a girlfriend, a loan shark, three children and a $300-a-day gambling habit.

"Wiseguy" is a one-gulp book. You will swallow it in one sitting and then will want to shower to wash away the sense of grime. It calls to mind Joseph Conrad's novel, "Nostromo," set in South America amid a "mire of corruption that was so universal as to almost lose its significance." But Hill's country is the United States.

Hill calls police payoffs "wiseguy scholarships" that send cops' kids to college. Wiseguys get special treatment in prison, cooking pasta and red snapper in their quarters. And just when you are ready to disbelieve such stories, The New York Times runs his story: "Federal authorities charged two prisoners yesterday with arranging heroin sales from pay telephones in a penitentiary in Lewisburg, Pa." Of course wiseguys only go to prison if they cannot "reach" juries. Hill explains, patiently:

"Everybody reaches the jury. It's business and it's easy. During the jury selection, for instance, your lawyer can find out everything he wants to know abut a juror -- where he works, lives, family status. . . . The 'where he works' is what interested me most. Where a guy works means his job, and that always means the union, and that's the easiest place to make the reach."

Pileggi is a dispassionate scientist putting a drop of brackish swamp water, teeming with low life, under a microscope. What you see is a crushing refutation of all the facile talk about curing all crime by erasing the "root causes" of crime, causes such as bad social conditions. Hill was a criminal for rational and passional reasons: crime paid well and, more important, he loved the life.He liked the camaraderie and the status. And the stealing: he loved it. The "root cause" of much crime is . . . criminals, like Hill.

Look through Pileggi's microscope at Hill's best friend, Jimmy "The Gent" Burke. He named a son Jesse, after Jesse James. The day Burke got married, police found Burke's wife's former boyfriend's car. The boyfriend was distributed in a dozen pieces around the car. There is honor among such thieves. When they must "whack" (kill) a fellow wiseguy's son, they shoot him in the chest so the face will be unmarked and the casket can be open. Pileggi's book expands the reader's sense of the range of human motives.

Today, Hill is still testifying. He still is getting $1,500 a month as a government employee. He still is, in a sense, a wiseguy.