A suicidal Pace University student sparked a terror scare early yesterday when he was found wandering in a subway tunnel beneath the East River.

Aaron Fetto, 20 — wearing an orange reflector vest and other transit-worker gear and carrying a quart-size bottle of cyanide tablets — told cops he was looking for an “isolated place in the subway system” to kill himself.

Transit workers found him on the track for the 4 train between Brooklyn and lower Manhattan at 5:30 a.m., police sources said.