Two retired New York City police detectives, onetime partners who had long been suspected of ties to organized crime, were charged by federal prosecutors yesterday with taking part in eight murders on behalf of the Mafia - most while one or both were still active members of the police force.

The charges, detailed in an indictment unsealed in Federal District Court in Brooklyn, were among the most startling allegations of police corruption in memory. In one case, in 1990, prosecutors said the detectives, driving an unmarked police car, pulled over a Mafia captain on the Belt Parkway in Brooklyn and shot him to death for a rival mob figure. In another, in 1986, they flashed their badges and kidnapped a mobster, threw him in the trunk of their car and delivered him to a rival, who tortured and killed him.

"In a stunning betrayal of their shields, their colleagues and the citizens they were sworn to protect, Louis Eppolito and Stephen Caracappa secretly worked on the payroll of the mob while they were members of the N.Y.P.D," the United States attorney in Brooklyn, Roslynn R. Mauskopf, said at a news conference to announce the indictment.

For years, Ms. Mauskopf charged, the men had been paid handsomely for their role in the killings and for routinely funneling secret information about criminal investigations to other members of organized crime. In most of the killings, she said, they did not pull the trigger but helped other hit men track down the victims, at one point becoming so instrumental that they were put on the mob's payroll at $4,000 a month.

Mr. Eppolito, 56, who once co-wrote a book about his life as a police officer whose relatives were in the mob, and Mr. Caracappa, 63, who worked in a police unit that was responsible for investigating mob killings, were arrested on Wednesday night at an Italian restaurant in Las Vegas, Ms. Mauskopf said. Mr. Eppolito retired in 1990, Mr. Caracappa two years later.

For more than a decade, the men, while collecting their police pensions, have lived across the street from one another in an affluent gated community in Las Vegas, Mr. Caracappa working as a private investigator and Mr. Eppolito playing bit parts in nearly a dozen popular movies, including "Goodfellas" - portraying mobsters, hoodlums and drug dealers. They appeared in Federal District Court in Las Vegas last night, where an acting United States magistrate judge, Jennifer Togliatti, postponed an extradition hearing until today.

The charges, dramatic as they are, were not entirely surprising: the pair were investigated by the F.B.I. and the New York Police Department in 1994 after a Mafia informant provided officials with many details of the killings. But the informant, who prosecutors said had commissioned many of the crimes, was later discredited, and federal authorities at the time were unable to build a prosecutable case, officials said yesterday.

But now, with a new informant, whose name was not disclosed, and a team of what Ms. Mauskopf called tenacious investigators, several of them also retired city police detectives, the authorities were able to collect enough evidence over several years to persuade a grand jury to indict the men.

The former detectives were charged with a racketeering conspiracy, which includes their roles in the killings, two attempted murders, obstruction of justice, money laundering and other crimes. The indictment accuses them of working as secret associates of the Luchese crime family. They are charged with disclosing the identity of six cooperating witnesses - three of whom were killed - and compromising several federal and state investigations.

None of the eight murders charged in the case - all but one involving victims who were organized crime figures - occurred after the first, failed attempt to make a case against the men.

Mr. Eppolito's lawyer, Richard A. Schonfeld, said his client "absolutely denies the charges" and cited what he called an exemplary 21-year police career, with 107 medals, including several for valor, in arguing that he should be released.

Edward Hayes, a lawyer in New York who represented Mr. Caracappa when he was under investigation more than a decade ago, said he was shocked at the charges. He said the mob figure who made the accusations at that time, Anthony Casso, was "a homicidal maniac" and "a raving lunatic." He said his client, a Vietnam combat veteran who retired as a first-grade detective, had denied the allegations before.

The charges against the two men, who face up to life in prison if convicted, will be resolved over the coming months, or perhaps years, in Federal District Court in Brooklyn. But the accusations themselves are a bizarre and breathtaking chapter in the history of corrupt police officers, mobsters and murder.

Both men joined the force in 1969, a year in which the city, with abbreviated background checks, hired an unusual number of officers who were later arrested or fired. Mr. Eppolito had relatives in organized crime - his father, Ralph, was called Fat the Gangster and his uncle, James, was known as Jimmy the Clam. But Mr. Eppolito did not disclose any of that on his police application.

He went on to serve as a patrol officer and detective, working in the Brooklyn Robbery Squad and in South Brooklyn. And after he retired, he wrote, with Bob Drury, "Mafia Cop: The Story of an Honest Cop Whose Family Was the Mob," in which he chronicled what he said were wrongful accusations brought by the Police Department that he sold information to the mob. Mr. Eppolito was cleared of charges brought against him by the department in that case in 1985.

Mr. Caracappa, who was Mr. Eppolito's partner in the robbery unit, went on to join the department's prestigious Major Case Squad, where he helped form the Organized Crime Homicide Unit. There, he specialized in the Luchese family and served as a clearinghouse on police and F.B.I. investigations into all mob killings, collecting information. It was information, prosecutors now allege, that he sold to members of the Mafia - revealing the identities of confidential informants, wiretaps and pending cases. In one instance, the information allowed Mr. Casso and the Luchese family boss to flee before they were indicted.

One of the killings involved a case of mistaken identity. Mr. Casso, eager to avenge an attempt on his own life in 1986, asked the two detectives to track down a Gambino family soldier named Nicholas Guido, according to prosecutors. But when Mr. Caracappa used a Police Department computer database to find an address for the man, he retrieved the address for the wrong Nicholas Guido, according to prosecutors, and instead turned over the address of an innocent man who officials said was mildly retarded.

Mob killers found the wrong Mr. Guido outside his home on Christmas Day 1986. They shot and killed him.

Joe Schoenmann, in Las Vegas, contributed reporting for this article.