Steve Rannazzisi -- I Only Had 15 Seconds to Change My 9/11 Lie

'League' star Steve Rannazzisi admits he did a "terrible" thing by lying about 9/11, but says the lie was not premeditated ... it started at an off the cuff quip at The Comedy Store.

Steve went on Howard Stern's show Tuesday and explained his lie ... that he was in one of the Twin Towers during the attack and it became a life-changing moment that led him to pursue his career in comedy.

According to Steve, he was just asked by someone at the club where he was during the attack and the phony story just spilled out. He says once that happens you have 15 seconds to say it was BS or else you have to own it.

It's a really good interview. He says he chose to talk about his lie on 'Stern' because Howard personifies New York and felt it was the right venue.