A Cuban-born FBI agent told a jury in a mob case yesterday that his undercover act as an Italian American played so well in the Gambino crime family that he won over an ailing Gambino captain who distrusted strangers.

Within months of meeting Gregory DePalma, agent Joaquin Garcia found himself being romanced Gambino style.

“You never been with any wiseguys before, right?” DePalma could be heard asking the agent on a tape of a June 2003 conversation played in U.S. District Court in Manhattan.

When Mr. Garcia said he had not, DePalma promised him benefits: “Nobody could bother you. Nobody could come near you, no wiseguys, nothing. I don’t care if they’re the boss, the underboss of another crew.”

Mr. Garcia said he was honored.

Capping a 30-year FBI career, Mr. Garcia spoke before an anonymous jury in a courtroom that was ordered closed to protect his identity and prevent people from seeing him. Testimony and the recordings were played in a room outside court for reporters.

“I played the role of being Italian, fourth or fifth removed from Sicily,” Mr. Garcia said as he introduced his lead part in the racketeering trial of the 74-year-old DePalma, who once boasted that he was the fourth most powerful Gambino. “I was posing as Jack Falcone, or Big Jack.”

Mr. Garcia said he retired from the FBI two months ago after spending 24 years of his three decades in the FBI in more than 30 undercover operations in probes into terrorism, drugs, police corruption, murder for hire, and organized crime.

He said DePalma came onto his radar screen after he was asked to pose as an investor at a Bronx topless dance club owned by a friend of the DePalma family who was cooperating with the government.