Aging, ailing, and broke, Genovese gangster Federico “Fritzy” Giovanelli reported to a federal prison hospital this week clutching a small duffel bag and a deep, dark secret that has haunted the FBI and federal prosecutors for more than two decades.

Giovanelli, 72, is beginning a 10-year obstruction of justice rap for alerting DeCavalcante mobsters that they were about to be indicted in 1999.

It wasn’t the first time that Giovanelli got hold of some top-secret intelligence about what the feds were up to. In 1982, the FBI learned from a top-echelon informant that Fritzy had tipped John Gotti’s right-hand man in crime about a bug the bureau had planted in his home. Fritzy’s timely tip cut short a major heroin probe.

As if that wasn’t bad enough, Giovanelli later beat murder charges in the shooting death of Detective Anthony Venditti, who was gunned down while tailing Giovanelli in Queens.

Not surprisingly, authorities turned up the heat on the cagy Genovese gangster, managing to send him to prison three times over a 15-year period for gambling, loan-sharking, and a parole violation.

But try as they might – and they tried everything – the feds never figured out where he was getting his dead-on information about law enforcement activities. And therein lies the secret he carried to the prison hospital in Butner, N.C., on Tuesday.

All the feds know now is what they knew 23 years ago: Giovanelli somehow managed to obtain a draft copy of an FBI affidavit detailing a bug that agents had installed in the home of Gambino soldier Angelo Ruggiero.

At the time, the FBI was deep into a seven-month heroin trafficking probe involving Ruggiero, Gotti’s brother Gene, and other wiseguys. Without warning, the wiseguys abruptly stopped meeting in the basement of Ruggiero’s Cedarhurst, L.I., home to talk about their booming drug business.

FBI agents knew immediately that their investigation had been blown. Wiseguys had talked openly for months about their operation. “There’s a lot of profit in heroin,” Ruggiero blabbed on June 18.Then they stopped showing up. The FBI sought out its key Gotti crew mole, Wilfred “Willie Boy” Johnson. Willie Boy quickly fingered Giovanelli as the culprit, but said he didn’t know Fritzy’s source.

The FBI looked at clerical workers in the Brooklyn Organized Crime Strike Force. Then they focused on their own office, including agents and support staff, searching for any connection to Fritzy. After finding the draft copy of an affidavit used to renew the bug in the attic of a Gotti pal, agents investigated informant reports that an inebriated agent had left the document in a bar near the FBI office in Rego Park, Queens – to no avail.

Still desperate to figure out Fritzy’s secret, the feds tapped his phone from late 1985 to early 1986. While they learned many other fascinating things, Fritzy never said a word linking him to the recovered draft copy, news of which had been leaked to reporters in an effort to stimulate discussion about the case.

What emerged from the tap were secret deals involving corrupt activities of the Brooklyn Democratic County leader at the time, Meade Esposito, a close Giovanelli pal, and Rep. Mario Biaggi of the Bronx. Esposito and Biaggi were later convicted and jailed.

The taped conversations also yielded a treasure trove of often hilarious chatter between Giovanelli and mob cohort Frank “Frankie California” Condo about food, recipes, diet, vitamins, getting old, the “10 O’clock News,” their girlfriends and wives, and much more. Intrigued readers can listen to their banter on the Smoking Gun Web site.

But no one learned Fritzy’s source then, and no one knows who it is today. After the feds filed an indictment charging Giovanelli with obstructing justice in 1999, a former New York FBI boss, Barry Mawn, said the source was a woman “contract employee of a stenographic service that is periodically utilized by the [Manhattan] U.S. Attorney’s office.”

In court papers and at Giovanelli’s trial, however, prosecutor John Hillebrecht told Federal Judge Jed Rakoff that while there is “circumstantial evidence” that the suspect was a woman stenographer, the feds have “no concrete specific evidence of who it is.”

The prevailing wisdom of law enforcement authorities is that the same corrupt source was behind the information Giovanelli provided to the Gambinos in 1982 and the DeCavalcantes in 1999.

“There’s no doubt in my mind it’s the same person,” a law enforcement source said. “It’s no coincidence that Fritzy turns up in two similar schemes 20 years apart. The scary thing is we don’t know if other cases were compromised, ones we never heard about.”

Giovanelli’s attorney, Vivian Shevitz, says it doesn’t matter who gave her client the information.

“My client is as guilty of a crime as Jerry Capeci or any other reporter who gets information about a grand jury investigation and then reports it,” said Ms. Shevitz, equating Fritzy’s conduct, including the protection of his sources, with that of good journalists.

“This conviction is a complete miscarriage of justice,” said Ms. Shevitz, who will appeal the conviction with the Second Circuit Court of Appeals next month. She insisted that prosecutor Hillebrecht framed her client by coaching two DeCavalcante turncoats to alter previous testimony they had given about Fritzy’s tip to include an offer by him to kill the informer who had cooperated with the feds if the DeCavalcantes couldn’t do the job.

“If the courts allow this to stand despite their continuously shifting testimony, we might as well close up shop on the idea of due process and basic fairness. What they’ve done here,” she said, “is convict him of the murder for which he was acquitted after four trials, the killing of Detective Venditti.”

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Although the feds failed to squeeze Giovanelli’s secret out of him, they did hurt him in the pocketbook.

During the three years between his initial obstruction of justice indictment and his trial last year, prosecutors upped the ante, hitting him with racketeering charges that included extortion and running a stolen-auto parts operation in Brooklyn. His funds ran out, and, under provisions of the Criminal Justice Act, his lawyers’ fees were paid by the court.

When the jury acquitted him, Fritzy quickly conceded that $20,000 that had been seized as part of the “chop shop” operation should reimburse CJA funds that had gone to his lawyers. His wife, Carol, who has lived a “largely separate” life in their Middle Village home of 42 years, felt differently about $41,400 that was seized from her bedroom.

In court papers, Ms. Shevitz noted that a detective had reported finding the money in Mrs. Giovanelli’s bedroom “in a statue stand” where she had hidden it. As expected, Mr. Hillebrecht objected.

A month later, Mr. Giovanelli wrote Judge Rakoff and gave up her claim to the money “to support my husband,” rather than fight what she believed would be another losing battle. “In the last case,” she said, “they kept money taken from my children as well as my husband.”