CHICAGO – The brother of reputed mob boss James Marcello pleaded guilty to racketeering and other charges Thursday and admitted he paid a witness $4,000 a month to keep silent about unsolved underworld murders.

Michael Marcello, 56, of Schaumburg, was one of three men to plead guilty in the case before federal Judge James B. Zagel on Thursday, five days before Chicago’s biggest mob trial in years is scheduled to start.

Marcello, in leg irons, listened as lead prosecutor Mitchell A. Mars accused him of paying former mobster Nicholas Calabrese $4,000 a month in hopes that Calabrese would not talk to federal agents and tie his brother to the killings. Mars did not say how long Marcello paid the money.

Among the victims: Tony “The Ant” Spilotro – the Chicago mob’s onetime man in Las Vegas, who was found buried alongside his brother in an Indiana cornfield. The Ant inspired the Joe Pesci character in the movie “Casino.”

When asked by the judge, Marcello said Mars was telling the truth.

James Marcello, described by prosecutors as the head of a street crew of the so-called Chicago Outfit, is one of eight men due to go on trial in the case, which arose from the FBI’s Operation Family Secrets probe of long-unsolved murders. Jury selection starts Tuesday.

Other defendants include such reputed mobsters as Frank Calabrese Sr. and Joseph “Joey the Clown” Lombardo, who was captured after a nine-month federal manhunt after the indictment was unsealed.

The eight men have pleaded not guilty.

Michael Marcello pleaded guilty to racketeering, conducting an illegal gambling business, hiding profits from federal tax collectors and obstruction of justice by paying Nicholas Calabrese to keep mum.

Calabrese, brother of Frank Calabrese Sr., ended up talking to the FBI and now figures to be the prosecution’s star witness. He is expected to tell an extraordinary history of the mob from the 1960s almost until now.

Michael Marcello faces a maximum sentence of 35 years in prison, although the actual term is likely to be much less. A sentencing date was not set, and no obligation to testify against his brother was spelled out in his plea agreement.

Also pleading guilty were Thomas Johnson, 52, of Willow Springs, and nephew Dennis Johnson, 36, of Plainfield, both of whom worked for Michael Marcello’s M&M Entertainment of suburban Cicero.

The two acknowledged they altered video games so they could be used as gambling devices, placed them in taverns and clubs, and collected the proceeds. Bogus records were created to hide the profits, they said.

Thomas Johnson faces a maximum sentence of 10 years, and Dennis Johnson five years, although federal guidelines call for lesser penalties.