NEW YORK -- An undercover FBI agent posing as a wiseguy infiltrated the Gambino organized crime family--once run by the late John Gotti--with an act so convincing he was considered for membership, authorities said Wednesday.

"Had we left him out on the street much longer, the Gambino family ranks would actually have increased by one," Pasquale D'Amuro, head of the FBI's New York office, said at a Manhattan news conference announcing 32 arrests in a racketeering investigation.

The unidentified agent "risked his life as a mole for the better part of two years after he was put on record" as a family associate, said U.S. Atty. David Kelley.

Among those named in a 53-count indictment were alleged Gambino boss Arnold "Zeke" Squitieri, 69, and reputed underboss Anthony "The Genius" Megale, 51.

Officials said Squitieri, a protege of Gotti, the "Teflon Don" who died in prison in June 2002, took over as acting boss after Gotti's brother Peter was convicted in two trials last year.

Prosecutors said the undercover investigation was the most effective since FBI agent Joseph Pistone infiltrated the mob in the 1980s, taking on the identity of "Donnie Brasco" and bringing down the leaders of the Bonanno crime family.

Wednesday's indictments allege extortion, loan sharking, illegal gambling and other crimes, including a beating in the housewares department at a Bloomingdale's store. The mobsters met at a nursing home to plot some of their crimes, court papers said.

The indictments of Squitieri, Megale and the others "rip out at the roots the first post-Gotti Gambino hierarchy," Kelley said.

Squitieri was awaiting arraignment in federal court in Manhattan; a call to his attorney was not immediately returned. Megale, already in custody on a separate racketeering indictment in Connecticut, denies he's the underboss, said defense attorney Stephan Seegar. Both defendants face up to 20 years in prison if convicted.

D'Amuro credited the undercover agent with making hundreds of secret recordings revealing the family's inner workings.

Like Donnie Brasco in the 1980s, the agent "was told by a high-ranking member of the crime family that he would be proposed for induction," D'Amuro said.

The mobsters used threats of physical and economic harm to force a New York City radio station to provide free ads for businesses in which the criminals had a financial interest, Kelley said. Death threats and beatings were used to extort money from a restaurant owner in Greenwich, Conn., construction companies in New York and a New Jersey trucking company, among others, the indictments said.

The family's violence turned inward at one point, Kelley said, when some of the defendants publicly beat a "recalcitrant member" with a candlestick at a Bloomingdale's outlet in suburban White Plains.

In another incident, members of the family "extorted money from a victim to pick up the tab at the Venetian Hotel for their wives for a jaunt in Las Vegas," Kelley said.

He said the undercover agent "risked his life" working under Gregory DePalma, identified in the indictment as a captain in the Gambino organization. The DePalma crew tried to hide their plans by meeting at the bedside of DePalma's son, comatose after a failed suicide attempt, at the United Hebrew Geriatric Center in New Rochelle, Kelley said.

"They saw this as a safe harbor," Kelley said. "Who's going to have the audacity or lack of grace to go into a nursing home and surveil them? Well, we certainly did."

The undercover agent and electronic eavesdropping, including phone taps, enabled prosecutors to learn about incidents of union corruption, illegal gambling and loan sharking, Kelley said.

"This is a case where this hierarchy was in place for a very short period of time before we swooped in and were able to get them out," he said.

The late John Gotti was a key figure in the rise of Squitieri and Megale.

Squitieri, of Englewood Cliffs, N.J., was released from federal prison in 1999 after serving 11 years on a drug conviction. Gotti, already imprisoned, promoted Squitieri to capo. Gotti brought Squitieri into the family after the 1985 slaying of Paul Castellano.

According to court records, Squitieri killed Gambino soldier Liborio Milito, one of five murders Gotti was convicted of ordering.

"John always liked Squitieri," a government source said. "They drank together; they played cards together."

Megale, of Stamford, Conn., infuriated Gotti in 1990 when he pleaded guilty to racketeering and acknowledged in the plea that he was a member of an organized crime family. Megale received close to 6 years for that offense.

In September, Megale was charged with racketeering and extortion, accused of shaking down a Stamford nightclub owner and a vending machine operator. Megale allegedly told the nightclub owner he had to pay $2,000 a month--plus a "Christmas bonus."

Though Megale denies he is the No. 2 man in the Gambino crime family, prosecutors played a 2002 FBI surveillance tape in which Megale was heard telling a friend, "They made me the acting underboss. So I'm over everybody."

Megale's defense attorney said that statement and others were taken out of context.