In Junior's delicatessen in Brooklyn, an undercover agent, wired for sound, met a gangster in the men's room to pick up a $5,000 bribe.

"It's under the commode," the gangster said.

The agent reached under the top of the toilet tank, pulled out a packet of bills and gasped, "Just like in the movies!"

The tape of the meeting was played last week at the trial of Carmine (The Snake) Persico, alleged boss of the Colombo organized-crime family. A few days earlier, James Caan, the Hollywood actor who portrayed the eldest son of Don Corleone in "The Godfather," showed up at the trial, kissed Persico on the cheek and declared himself a lifelong friend of one of Persico's codefendants.

Federal marshals promptly served Caan with a subpoena.

In the hulking U.S. District Court House on Foley Square, fact these days is as strange as screenplay. Three major Mafia trials are taking place here, involving 42 defendants -- the largest assemblage of alleged organized-crime leaders ever to be prosecuted at one time and in one place.

"The greatest mob show on earth," declared one columnist. School children in civics classes flock to hear testimony about blood oaths, shopping bags filled with cash, bodies stuffed into cement drums and "men of honor" with nicknames such as "Big Paul," "Frankie the Beast," "Andy Mush" and "Beansie."

This spring, the reputed chieftains of the city's five powerful organized-crime families -- Gambino, Genovese, Bonanno, Lucchese and Colombo -- will go to trial on charges that they control a nationwide commission of organized-crime families that has operated since 1931.

The New York trials are the culmination of a huge federal and state assault on organized crime's most powerful base. According to the Federal Bureau of Investigation, half of the nation's roughly 2,000 organized-crime members and their 20,000 associates live in the New York area. About 300 suspects are under indictment in federal and state organized-crime cases here.

Major trials are also under way in Kansas City and Boston, as part of what prosecutors say is the most intense nationwide crackdown on organized crime in history.

In Boston, U.S. Attorney William Weld is prosecuting reputed Mafia boss Gennaro Angiulo and other family members on racketeering charges. The Kansas City case involves mob operations and Teamsters Union corruption in Chicago, Cleveland, Milwaukee and Las Vegas.

"If we continue to operate like this for the next five or six years, there's a real chance we can crush the Mafia as an organization," said Rudolph W. Giuliani, U.S. attorney for New York's southern district, who will prosecute the commission case.

"If we stopped now," he added, "and just tried the cases we've brought so far, in a short while things would be back to normal" because new leaders would take over.

Behind the crackdown is a dramatic change in political attitudes toward the cohesive groups that call themselves -- on wiretaps and in court testimony -- "La Cosa Nostra" or the Mafia.

Giuliani, a Brooklyn-born Italian-American, was an assistant U.S. attorney here in 1971 when then-Attorney General John N. Mitchell ordered the Justice Department and the FBI to refrain from using the words "Mafia" or "Cosa Nostra." The directive came a few months after Joe Colombo's Italian-American Civil Rights League organized a demonstration of 100,000 people at Columbus Circle to protest use of the terms.

"There was a political fear," Giuliani said. "Everyone knew there were these five families, but the pressure was designed to instill self-doubt . . . . The really sick thing was that Joe Colombo was head of an organized-crime family."

However, beginning under President Jimmy Carter and intensifying under President Reagan, the Justice Department targeted organized crime with greater personnel, more money and wider use of court-ordered bugs and wiretaps.

A federal antiracketeering statute passed in 1970 was broadly interpreted by the Supreme Court in 1981 to allow convictions of previously shielded organized-crime leaders on grounds that they supported or benefited from criminal enterprise.

While the prosecutions involve gambling, narcotics, car theft, embezzlement, murder, loan sharking and other traditional criminal enterprises, they are also directed toward illegal infiltration of legitimate businesses. "It is pretty hard to think of an industry in New York that organized crime is not involved in," said Ed McDonald, chief of the Justice Department's organized-crime strike force in Brooklyn.

McDonald successfully prosecuted high-ranking members of the Genovese and Lucchese families, as well as union officials, for bid-rigging and fraud in the drywall industry. He obtained the indictment of Philip (Rusty) Rastelli, the Bonanno family leader, and Teamsters officials for corruption in the moving and storage industry. He obtained the indictment of Lucchese family leaders and officials of a Teamsters local on charges of controlling the air-freight industry at Kennedy airport.

Members of the five mob families also have been convicted or are under indictment for criminal infiltration -- often through union officials -- in the restaurant, food-distribution, entertainment, jewelry, garment, trucking, construction, waste-disposal, funeral home, real estate, liquor, vending and waterfront-cargo industries in the New York area.

The three trials now in progress feature evidence of the usual grisly murders and seedy deals. But rarely has the public been treated to a cast of such colorful characters, to testimony so redolent of romantic lore and titillating detail, and to tales of such derring-do.

In the Persico trial, Frank Melli, an alleged captain in the Colombo family, is accused of arranging to cut off electricity to the entire town of Carlstadt, N.J., in November 1979 to facilitate the burglary of $2.2 million worth of Swiss watches at a warehouse. Police communications were disrupted during the blackout.

Persico and his associates, along with Ralph Scopo, the recently retired president of the Concrete Workers District Council, also are charged with a multimillion-dollar extortion scheme involving 1 percent payoffs to the Colombo family on concrete contracts for major building projects.

In a moment of high courtroom drama last week, Scopo clutched his heart, staggered to the jury rail and was taken to the hospital, where an emergency room spokeswoman pronounced him "fine."

Courtroom regulars were unmoved, however, remembering that when the commission indictments were returned in March, three alleged mob chieftains had to be hospitalized suddenly for chest pains.

Persico, who served 14 years in prison on a truck-hijacking conviction, fled after the recent indictment and was captured after making the FBI's 10 Most Wanted list. He has pleaded not guilty, as has Gennaro (Jerry Lang) Langella, alleged acting boss, and the other defendants.

Langella's attorney, David Breitbart, gestured toward the burly dark-suited defendant and told the jury that he is "swaddled in the bandages of innocence . . . . Look at my client's face. Is this a terror?"

Some of the most lurid testimony has come in the trial of Paul (Big Paul) Castellano, reputed head of the Gambino family, and nine other family members and associates.

The trial is the first to come out of a 78-count indictment charging Castellano and 20 other defendants with various crimes, including car theft, extortion, narcotics trafficking and 24 murders. Castellano and the other defendants have pleaded not guilty.

"These are not the kind of individuals that you would . . . go to a garden party with," Assistant U.S. Attorney Walter Mack told the jury.

But the government's star witness, admitted murderer and car thief Vito Arena, is hardly the garden-party type either.

Arena, who has spoken to a literary agent about writing a book and has told prosecutors he wants Tom Selleck to portray him in the movie version, described how, after shooting two car dealers, he sent out for pizza and franks while the bodies cooled sufficiently to be dismembered.

Arena, 43, a jowly man dressed in a conservative blazer, gray slacks and tinted glasses, said he testified to obtain leniency for his male lover who was his accomplice. He also acknowledged that he had asked prosecutors to pay for plastic surgery and had demanded a barber chair and Bruce Springsteen records while in jail.

In the third trial, known as the "Pizza Connection" case, spectators must walk through a metal detector to enter the courtroom. Gaetano Badalamenti, reputedly the former head of the Sicilian mafia, and 21 others, including leaders of the Bonanno family here, are charged with running a $1.6 billion international heroin-smuggling operation, laundering some of the money through pizza parlors -- as well as through Merrill Lynch and E.F. Hutton accounts.

The defendants have pleaded not guilty. One of the defense lawyers said the prosecutor had "fabricated a story -- a movie script."

So far, much of the testimony has been in Italian as Tommaso Buscetta, the highest Cosa Nostra leader to cooperate with Italian police, described the commission that Badalamenti allegedly ran. In his initiation, Buscetta said, his finger was pricked, and he rubbed the blood onto a picture of a saint. He set fire to the picture and took an oath that "should I betray the organization, my flesh would burn like this saint."

Soft-spoken and "exquisitely patrician," as columnist Murray Kempton described him, Buscetta has been dubbed "King Rat" by the city tabloids, which have reveled in his testimony that he had three wives in different countries.

All of the trials have anonymous juries -- a measure Giuliani says provides extra security as some of the defendants have been involved in jury tampering in the past. However, Richard Emery, staff counsel of the New York Civil Liberties Union, and some other attorneys have criticized the withholding of jurors' names as "extreme."

"Carefully orchestrated news conferences, press releases and luridly phrased indictments have prejudiced the accused in the eyes of the public and potential jurors," Emery charged in an op-ed piece in The New York Times. Use of nicknames such as "The Snake" or "The Bulldog" are unfair, he added, and he called Giuliani "an overeager prosecutor."

Defense lawyers attribute the prosecutions to Giuliani's political ambition. "This is sensational stuff," Breitbart said. "The attitude is to use the media as an extra juror. Giuliani has choreographed these trials. If Gov. Mario M. Cuomo runs for president, there will be an Italian-American vacancy in the gubernatorial spot."

Giuliani said in an interview that the timing of the trials was accidental and that he has no political plans for the near future. He is confident that he will win convictions, he said.

In the long run, whether all the current defendants go to jail or not, the families face a different enemy. While other ethnically based organized-crime groups are emerging, such as the Colombian cocaine gangs and the Chinese Tongs, the traditional Cosa Nostra "is receding in power," Giuliani said.

"The demographics are working in our favor. The Italian-American neighborhoods hardly exist anymore where they were protected and considered to be heroes," he said. "Before, they recruited talented people who for sociological reasons didn't feel they could succeed in legitimate businesses. Now these people are in college, in medical school, law school and business school. They don't want any part of it."