More than 50,000 people were arrested last year in New York City for low-level marijuana offenses, according to the New York Division of Criminal Justice Services. Those 50,383 arrests represented 15 percent of all arrests by the New York Police Department. The 50,000-oplus figure is more marijuana arrests in one year than the number of similar arrests made by the New York Police Department over the entire period from 1978 to 1996, according to an analysis for the alliance done by Harry Levine, a sociology professor at Queens College.