A clueless tourist claiming to be a cop asked 9/11 Memorial security if he could bring in his gun — and when they said no, he hid it under a seat cushion in a nearby hotel lobby, sources told The Post yesterday.

He stashed the loaded .22-caliber pistol at the busy World Center Hotel on Washington Street.

“Somebody sat in the chair and they discovered the gun” at about 2 p.m., the sources said.