Hartford, Connecticut- Every brothel needs a madam, and at the Alpha Leisure & Health Club Inc. in Hartford, owner Gail Gaer played the role for a quarter-century, overseeing millions of dollars in prostitution transactions while trying to keep the true nature of the business a secret, prosecutors said.

“She definitely was one of the brains behind the operation,” said Kevin J. O’Connor, the U.S. attorney for Connecticut.

In the first of what is expected to be a series of crackdowns on people associated with the club, federal law enforcement officials announced Wednesday that Gaer, 63, had pleaded guilty to operating one of Hartford’s most sophisticated and persistent prostitution operations.

Gaer, a Newington resident who owned the club for 25 years before selling it in 2002, pleaded guilty in U.S. District Court in Hartford to charges of conspiring to use an interstate facility — specifically, interstate wires used to receive credit card payments from customers — to promote prostitution, money-laundering and conspiring to smuggle currency into the country. She faces up to 25 years in prison and fines totaling $750,000 when she is sentenced on June 11.

O’Connor said that Gaer made more than $5.4 million while operating the call-girl ring for 25 years. He said that the club, which employed hundreds of women and listed more than 4,600 clients, produced more than $5.3 million in gross receipts from 1998 to 2003 alone.

“This was an extensive operation that involved not just prostitution but also money-laundering and other crimes,” O’Connor said. “The bottom line is that it has been affecting the quality of life in that neighborhood for far too long.”

O’Connor said that Gaer agreed to plead guilty to the charges before the case was submitted to a grand jury for formal indictment. He said that the club has been closed for several months as the investigation has closed in on the ownership.

For years, the club — on Franklin Avenue, one of the city’s most famous South End thoroughfares — drew the wrath of angry residents who complained about persistent prostitution taking place inside, despite the fact that the club was billed as a health and fitness center. Even when the club seemed to have closed its doors temporarily after being targeted in a city raid on massage parlors in 1997, residents complained that men and women could still be seen walking in and out of the building at all hours.

Despite the arrests of various managers and prostitutes working in the club, city police were frustrated in their attempts to track down and prosecute the people who had ownership interests and were profiting the most from the call-girl ring, law enforcement officials said.

But several months ago, city police turned to federal officials to help close the club. The joint effort allowed law enforcement officers to track credit card payments made by “customers” after visiting the club.

“The amount of time and resources that went into this operation was just incredible,” said acting Hartford Police Chief Mark R. Pawlina.

By tracing the payments to various banks and financial processing centers, law enforcement officials learned that, on average, customers were making “house fee” payments of $40 for 30 minutes with a prostitute, $50 for 45 minutes or $60 for an hour, according to court records that detail the records of Gaer’s guilty plea.

Prostitutes would also receive a “tip” from their customers worth at least the house fee, usually more, according to the records of the plea. If the tip was included in the customer’s credit card payment, the club would pay the amount to the prostitute in cash, minus 6 percent for the brothel, the court records say.

More often, however, customers would pay the tips in cash while charging the house fee on a credit card, thus making it appear on records that the money was spent on a legitimate massage or other health club service, O’Connor said.

To keep their profits hidden, Gaer and other interest-holders in the club — who have not yet been identified because they are part of the ongoing investigation — arranged to deposit millions of dollars in Swiss bank accounts, the records say.

In March 2001, the records say, Gaer went to Geneva and tried to withdraw more than $1 million in cash, but was only able to take out $60,000 while the balance was paid out in $200,000 checks. She then transferred the money into another Swiss account, the records say.

Later that year, Gaer and other interest-holders placed cash payments of more than $10,000 each in various mailing containers, and mailed them to co-conspirators throughout the U.S., the records say. The money was shipped and received without being discovered by customs or postal officials, the records say.

The front doors to the club at 156A Franklin Ave. were closed Wednesday, and Gaer’s attorney, Hubert Santos of Hartford, was not available to comment on her guilty plea. Gaer, who is free after posting bail of $250,000, was not available for comment, and her son, Brian, declined to comment after being reached by telephone Wednesday.

“This is something we’ve been waiting to see for seven years,” said Hyacinth Yennie, a neighborhood activist who has long encouraged city officials to shut down the club. “I’m really glad to see the authorities doing something.”

Pawlina said that city police, along with public health and other city officials, have closed the club in numerous raids and crackdowns through the years. But each time, the club would make whatever changes were necessary to correct any violations, and there was nothing to prevent it from reopening.

“The key was finding out who was behind it all, and that really required the involvement of the federal authorities,” he said.