George Grasso, the NYPD’s second in command, is leaving the department after more than 30 years to pursue a judicial appointment, officials said yesterday.

Grasso, 52, is the department’s longest-serving first deputy commissioner, and is responsible for running the force when Commissioner Ray Kelly is absent or unavailable.

On 9/11 and for several months afterward, Grasso was assigned as Kelly’s chief representative at the FBI’s New York command post.

Grasso was admitted to the New York bar in 1985.