Joseph Demarest Jr/fbi photo

WASHINGTON — Joseph M. Demarest, Jr., the head of the New York FBI, the agency’s largest office, is under internal investigation in connection with an alleged affair he had with an underling in management, sources familiar with the situation told ticklethewire.com., which first reported the story.

Demarest, who has headed the New York office since January 2009,  has been temporarily assigned to headquarters in Washington while the Office of Inspector General and the Office of Professional Responsibility look into the matter, sources said.

Demarest (far right) with Pres. Obama and FBI Dir. Robert Mueller/fbi photo

As a key part of the probe, according to sources,  investigators are trying to determine how truthful Demarest  was about the matter when he was questioned about it internally.  A website Main Justice reported that his version differed from the woman he had the affair with, and that the probe had been going since January.

A confirmed misconduct in the bureau can result in action ranging from a reprimand to a firing to a forced resignation or a demotion.

It is fairly common for high-ranking FBI officials in the field to be brought back to Washington on a temporary assignment while they are  under internal investigation.  In the past, some of those officials were eventually cleared of wrongdoing.

Demarest began his career with the FBI in 1988 after serving as a Florida sheriff”s deputy for five years. An FBI press release in 2006 said he was married with two children, but he reportedly is no longer married.

Demarest, through a spokesman, declined to comment Thursday.

Michael P, Kortan, the FBI’s chief spokesman, declined to comment on the report. However, he emphasized that Demarest remains in charge of the New York office.

He also said that Demarest was on temporary assignment in Washington to help further develop an FBI management system known as Strategy Performance Sessions (SPS). The program helps monitor and evaluate investigative programs, with an emphasis on the collection of intelligence.

He said Demarest was one of the people who helped originally develop the program for the FBI and his office in New York was noted for having a strong SPS management program.