Among the pretty large population of white people who have used pot and not been arrested for it is Mayor Michael R. Bloomberg. Asked during the 2001 campaign by New York magazine if he had ever smoked it, Mr. Bloomberg replied: “You bet I did. And I enjoyed it.” After he was elected and his remarks were used in advertisements by marijuana legalization advocates, Mr. Bloomberg said his administration would vigorously enforce the laws.

The statistics cited in the report, which were drawn from records kept by the New York State Division of Criminal Justice Services, show that Mr. Bloomberg has kept his word. Although low-level marijuana arrests last year are down from their peak in 2000, they remain at very high levels historically.

In an official comment on the study, the Police Department was critical of the role played by the New York Civil Liberties Union in publicizing the report and noted that the research had been backed, in part, by the Marijuana Policy Project, which supports legalization.

Paul J. Browne, the department’s chief spokesman, said that all crime in the city had declined by about 60 percent in the three decades cited in the study. “Attention to marijuana and lower-level crime in general has helped drive crime down,” Mr. Browne said.

Mr. Levine said that the only research on the issue suggested that marijuana arrests played little role in driving down serious crime, and may in fact divert police resources.

What of the skewed numbers on arrest by race? Mr. Browne said that it was wrong to use national drug use surveys as evidence of racial bias in New York marijuana arrests. Mr. Levine said that one reason black and Latino men were disproportionally arrested on marijuana charges is that they are the vast majority of those stopped and frisked by police.

More than 30 years ago, legislators and the governor agreed, in broad terms, that the state would no longer jail people in possession of small amounts of marijuana.