A retired police officer, described by prosecutors as a ringleader in a huge scheme to defraud the Social Security Administration, pleaded guilty on Friday and agreed to testify against his former colleagues in return for a reduced sentence.

Prosecutors said the former officer, John Minerva, 62, of Malverne, N.Y., was one of four men who helped scores of former police officers, firefighters and others swindle disability benefits from the government by pretending to have mental illnesses. Many of the applicants claimed to be suffering from depression and panic attacks because they had worked after the terrorist attack in New York on Sept. 11, 2001.

The four men coached the applicants to feign symptoms of depression and post-tramautic stress and steered them to two doctors to create false medical histories for federal authorities. Then they collected payoffs of more than $28,000 from each of the recipients once the government started sending them checks, prosecutors said.

More than 130 people this year were arrested and charged in three indictments with taking part in the scheme. At least 91 pleaded guilty. There are 38 open cases; eight cases were dismissed.