In one life, Billy Phillips was a dirty cop who walked his beat in high-shine Gucci loafers and mutton-chop sideburns.

Instead of working at a precinct, he worked 13 years toward his pension from inside the lone phone booth behind the dark-wood bar at the old P.J. Clarke’s at 55th Street and Third Avenue, putting drug dealers, pimps, prostitutes, and a menagerie of other unsavory criminals “on the pad” – old cop-speak for extortion.

“I never felt that the good Lord is that down on a hustler,” he liked to say.

In later years, Phillips would wear a wire as a star informant, incriminating mobsters and his fellow corrupt cops for the Knapp Commission, which led three decades ago to a host of reforms for the New York Police Department.

In another life, William Phillips, now 74, is state inmate #75-A-322. After losing a series of appeals in a murder case that went to the U.S. Supreme Court, he has been serving out a 25-to-life sentence.

Inside, he has become a jailhouse legend. Phillips has had one eye removed because of a cancerous tumor and is suffering from prostate cancer, but he has become one of the most active legal minds within the state’s penal system, having earned several legal certificates through programs for prisoners and, as a law clerk, operated the prison library. In exchange for his legal services, other inmates protect Phillips, because cops – even corrupt cops – have difficulty making allies in maximum-security prison.

Divorces. Criminal appeals. State court. Federal court. Habeas corpus. Real estate. Inmate grievances. Custody battles. Phillips says he has taken on cases for more than 500 inmates.

“Never in my wildest, wildest dreams did I imagine I would become a lawyer,” Phillips said during an interview with the magazine the American Lawyer more than 15 years ago.

“I was a knock around guy,” he went on. “Too busy having fun – money, skiing, flying, booze, broads. To me life was one big fun.”

In more than a quarter-century helping inmates fight legal battles, Phillips’s most futile effort has been his own. Three times he has applied for parole, and three times he has been swiftly rejected.

“You are a criminal of the worst kind whose danger to public safety is in the highest degree,” the parole board concluded of Phillips in its most recent decision, in September 2003. The board recommended he serve two more years, the maximum period before he again could seek release.

Now, however, that timeline might change. After losing his appeal to the parole board, Phillips filed a petition at state Supreme Court, requesting that it overturn the parole board’s decision. It was his third such request, and it was a long shot. Of the hundreds of petitions the court receives from prisoners seeking another shot at parole, experts said typically one or two are granted each year.

This month, Phillips became one of the chosen.

Justice Alice Schlesinger issued a scathing, unusually lengthy, 18-page decision calling the parole board’s rationale in its “brief, almost angry” decision against Phillips “wrong,” “perverted,” “contrary to the law,” and “arbitrary and capricious.” She ordered a new parole hearing immediately, and with different members sitting.

“If rehabilitation has any meaning, if there is a belief that a man can change, if there is a faith that the goodness of person can eventually resurface, then the law governing release on parole and the rationale for that law is being perverted by a Board that refuses to consider only what a man did 37 years ago and is paying for in almost 30 years in imprisonment,” Justice Schlesinger wrote.

The judge concluded: “Does the Board honestly believe that Mr. Phillips, a 74-year-old man, half-blind from cancer, who has helped countless people, and learned and taught the principles of law to many, truly is a continuing threat to society?”

A spokesman for the state’s Division of Parole, Scott Steinhardt, declined to discuss the Phillips case, citing continuing litigation. The state has 30 days to appeal Justice Schlesinger’s decision. A spokesman for Attorney General Eliot Spitzer, who represents the parole board, said attorneys had yet to decide whether to appeal.

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Once an incorrigible teenager from Queens, William Phillips followed in his father’s footsteps by joining the Police Department after serving in the Korean War. It was 1957, a time of gang warfare among leaders of New York’s five major Mafia families, and Phillips was a 27-year-old rookie looking to “score” extra cash and acceptance in the fraternity of a police department he claimed was corrupt “from top to bottom.”

Within three years he was “deeply involved in corruption,” Phillips told the parole board during his most recent hearing. “I was in a situation where I was on like a freight train going downhill,” he said.

The first time Phillips was implicated in a crime was in the early 1970s. He went to collect a payment from a young, slinky, blonde European madam, Xaviera de Vries, who had been paying Phillips protection money through a stocky electronics-surveillance salesman, Theodore Ratnoff, who acted as middleman between cop and madam – and was wearing a wiretap as an informant for the Knapp Commission. (The madam, as Xaviera Hollander, would go on to write the best-selling autobiography “The Happy Hooker.”)

Mayor Lindsay appointed the commission in 1970 following reports of widespread corruption within the Police Department. The goal of its chairman, the prominent attorney William Knapp, and its chief counsel, Michael Armstrong, was to uncover as much evidence of that corruption as possible. The strategy, as in many a criminal investigation: find the low-level perps and get them to turn against their bosses.

Phillips was the commission’s first major turncoat, Mr. Armstrong said, and its most effective one. He turned on the Police Department the same day he was approached by commission investigators, shortly after the tapes made with “the Happy Hooker.”

When the Knapp investigators came for him, Phillips was sitting on his normal stool at the back of the bar at P.J. Clarke’s, drinking a screwdriver with the former middleweight champion boxer Rocky Graziano.

“I knew it was all over,” Phillips would say of that moment. “A disaster.”

Mr. Armstrong, a prominent defense attorney who would later become Queens district attorney, said he never thought Phillips would turn. Getting Phillips to testify in open court would mean getting him to break the “blue wall of silence.” Looking to persuade him, Mr. Armstrong planned out a good-cop-bad-cop routine. He would let Phillips sit by himself in a room for a few hours with nothing to eat or drink and nobody to talk to, and then he’d come in with a cigarette. He’d rehearsed all the talk about “you can’t be a little bit pregnant.” And so on.

Phillips, it turned out, didn’t need coaxing. Mr. Armstrong remembered the encounter this way: “I walk in the office, and there’s Phillips in front of me, and he looks up and starts talking in that voice. … He says, ‘Listen, I’ve been sitting where you are sitting, and I’ve had people sitting where I am sitting. I know what I gotta do.'”

The next day Phillips went to work for the Knapp commission, wearing a wire, recording incriminating conversations with seven organized-crime figures, and he would eventually record no fewer than 69 deals on tape, Mr. Armstrong said.

Phillips’ problem was that he was a little too good an informant – or too visible. As he appeared on television at commission hearings, detectives investigating a five-year-old case of a prostitute and her pimp murdered on Christmas Eve spotted Phillips. They noticed that he matched the description of the alleged killer. There were other links, too.

The pimp had been paying Phillips bribes, and the detectives suspected Phillips might have murdered the man in a quarrel over money. Phillips said he was getting framed for ratting out fellow cops. He was arrested and charged with the double homicide after being identified by an eyewitness: the prostitute’s john, himself shot during the murders.

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In the legal drama that followed, William Phillips had a mistrial – the jury hung 10-2 for acquittal – and then a conviction, followed by several appeals. The lawyer who represented him before the U.S. Supreme Court, the civil-rights attorney William Kunstler, argued that the jury pool in Phillips’s second trial had been poisoned because one of the jurors had applied for a job at the district attorney’s office, a conflict of interest, and prosecutors failed to disclose the information. Prosecutors argued that one juror didn’t affect the result. The high court ruled against Phillips.

In prison, the former policeman has not been idle. He earned a bachelor’s degree from the State University of New York and a master’s degree from SUNY Buffalo with a straight-“A” record. At Attica, he even taught a course on legal research, and he received annual commendations for 17 years. He also served seven years on the Inmate Grievance Resolution Committee at the Auburn correctional facility; was chairman of the Lifer’s Committee for 15 years; was chairman of the Jaycees Criminal Justice Committee. He has already been offered a job after release: teaching a course on legal research at Manhattanville College in Westchester County. And in three decades in the prison system he has not been cited for one infraction.

Phillips, who declined to be interviewed by The New York Sun, currently is incarcerated at the Fishkill Correctional Facility, where correction records show he is studying commercial arts and works in the prison yard, for $1 a day, as a porter. The reason Phillips declines interviews is that he fears repercussions with the parole board, his lawyers said. After waiting in prison so long, being so old and so sick, Bill Phillips doesn’t want to take any more chances.

“There are two different people in me,” Phillips told the parole board in 2003. “One that came into here, in prison, that was involved in reprehensible conduct, and I think over the last 29 years that I have shown that I can be very adaptive to change. I think that I have changed my life around … I have been educated. I educated myself and I have been involved in every program that has been available to me. I don’t know what else I could possibly do while incarcerated to be able to gain parole.”