A vast network of Armenian gangsters and their associates used phantom health care clinics and other means to try to cheat Medicare out of $163 million, the largest fraud by one criminal enterprise in the program's history, U.S. authorities said Wednesday.

Federal prosecutors in New York and elsewhere charged 73 people. Most of the defendants were captured during raids Wednesday morning in New York City and Los Angeles, but there also were arrests in New Mexico, Georgia and Ohio.

The scheme's scope and sophistication "puts the traditional Mafia to shame," U.S. Attorney Preet Bharara said at a Manhattan news conference. "They ran a veritable fraud franchise."

Unlike other cases involving crooked medical clinics bribing people to sign up for unneeded treatments, the operation was "completely notional," Janice Fedarcyk, head of the FBI's New York office, said in a statement. "The whole doctor-patient interaction was a mirage."

The operation was under the protection of an Armenian crime boss, known in the former Soviet Union as a "vor," prosecutors said. The reputed boss, Armen Kazarian, was in custody in Los Angeles.

Bharara said it was the first time a vor _ "the rough equivalent of a traditional godfather" _ had been charged in a U.S. racketeering case.

Kazarian, 46, of Glendale, Calif., and two alleged ringleaders _ Davit Mirzoyan, 34, also of Glendale, and Robert Terdjanian, 35, of Brooklyn _ were named in an indictment unsealed in Manhattan.

Most of the defendants were to appear in court later Wednesday on charges including racketeering conspiracy, bank fraud, money laundering and identity theft.

Authorities began the New York-based investigation after information on 2,900 Medicare patients in upstate New York _ including Social Security numbers and dates of birth _ were reported stolen.

The defendants in the New York case also had stolen the identities of doctors and set up 118 phantom clinics in 25 states, authorities said. The names were used to submit fake bills for care that was never given, they said.

Some of the phony paperwork was a giveaway: It showed eye doctors doing bladder tests; ear, nose and throat specialists performing pregnancy ultrasounds; obstetricians testing for skin allergies; and dermatologists billing for heart exams.

In the New York portion of the case, more $100 million in fraudulent bills were submitted and Medicare paid out at least $35 million, sometimes by wiring it to the clinics' banks accounts, investigators said.

Most of the defendants "were Armenian nationals or immigrants and many maintained substantial ties to Armenia" and criminals there, the indictment said. Couriers would often carry cash proceeds from the fraud back to Armenia, it added.

Prosecutors were seeking forfeiture of real estate in Las Vegas; Palm Springs, Calif.; and elsewhere, and of a 2007 Maserati and a 2006 Jaguar.