A lazy Harlem cop is being probed for blowing off a subway rider who tried to give her a cellphone picture of a man she caught masturbating on the train, police said yesterday.

The uniformed officer at the 32nd Precinct told the woman, a civilian employee at the FBI’s New York office, that her complaint was not a police matter and told her to call 311 instead.

An NYPD probe has been launched and the cop was told she has to report to the Internal Affairs Bureau tomorrow, sources said.

The 41-year-old straphanger’s ride on an uptown 3 train got raunchy at about 3:45 p.m. Friday when the pervert boarded at Times Square, took a seat across from the woman and began to pleasure himself, police said. She managed to take a photo of the man with her cellphone camera before he exited at 96th Street.

The woman went right to the 32nd Precinct. She lodged a complaint and handed over the picture.

Then the clueless cop told her there was no crime and that it was a matter for 311, the city’s information and complaint hotline.

But “public lewdness” is a misdemeanor that results in hundreds of arrests each year.

“It was a police matter and IAB is investigating why anyone would have been told otherwise,” said police spokesman Paul Browne.

Police released the photo and asked the public’s help in catching the suspect. Officials also said the IAB is investigating how the woman was treated.

Transit cops interviewed the rider yesterday. “She didn’t have the [police] woman’s name but she described her,” said a police spokesman.

The straphanger’s plight recalled another subway rider, Thao Nguyen, who photographed a flasher on a train.

In 2005, Nguyen, then 22, was aboard an R train when a man boarded and masturbated. Nguyen left the train at 34th Street and reported the incident to a policewoman. The cop took down her information but didn’t want the photo. So Nguyen posted it online.

That flasher, Dan Hoyt, was arrested and sentenced to two years’ probation.

Nguyen later testified before a City Council committee that considered raising the penalty for public lewdness from 90 days in jail to a year.

Additional reporting by Larry Celona

philip.messing@nypost.com