A Washington Heights charity that aims to protect children from the dangers of lead poisoning is run by a man with a past conviction for attempting to obtain child pornography, The Post has learned.

Stephen Null, 64, head of Friends of Lead Free Children in Washington Heights, pleaded guilty in 2002 to attempting to obtain an image of sexual conduct by a child less than 16 years old.

Null served six years’ probation for the misdemeanor.

“It was a sting done by the Attorney General’s Office. I did not have child pornography, and that’s why the charge was reduced,” said Null.