Last night an unidentified man survived a suicide plunge from the Brooklyn Bridge after threatening police officers who were trying to talk him down. The 38-year-old man was approached by cops around 10:30 p.m as he clung to a girder about 35 feet away from the tower on the Brooklyn side. After waving a knife at them, he plunged to the East River, at least 120 feet below. Rescuers pulled him from the waters and rushed him to Lutheran Hospital, where his condition is not known. But police sources tell the Post investigators are checking the van with Jersey plates he abandoned at the scene to see if he left a note. And it's not unheard of for jumpers to survive suicide attempts on the East River bridges; in January a man jumped from the Manhattan Bridge, drifted to the Brooklyn shore, and walked away (photos).