Altering a Law the Police Use Prolifically On Tuesday afternoon, a 51-year-old black man was led into Manhattan Criminal Court to be arraigned on a charge that he broke a law that Mayor Michael R. Bloomberg has enforced with more vigor than any other: the possession of less than an ounce of pot. The day before, the police said, the man was seen walking along Second Avenue in East Harlem "publicly displaying" his little bag of weed. The man, whose identity is of no public interest, may be at the trailing edge of an era in which blacks and Latinos get in more trouble for having marijuana than do whites who have just as much. This week, the governor and the speaker of the Assembly said they supported a change in the law so that publicly possessing small quantities of pot would no longer be a misdemeanor. "This is primarily a young-person problem, about 60 percent," Gov. Andrew M. Cuomo said on Monday. And primarily, overwhelmingly, a problem for the black and brown community, 94 percent of the convictions. In a startling turnaround, both Mayor Bloomberg and Police Commissioner Raymond W. Kelly said that they supported the change in the law. Under Mr. Bloomberg and Commissioner Kelly, no other prohibition has been so vigorously enforced. About 400,000 people have been arrested over the last 10 years for breaking New York State Penal Law 221.10, which makes it a misdemeanor to openly possess or burn less than an ounce of pot. For the last four years, I have asked the mayor's office and the police commissioner why there has been an explosion of marijuana arrests among black and Latinos. Officials in those offices consistently, and ardently, defended the arrests as vital to public safety. In 2008, a police spokesman, Paul J. Browne, said there was no reliable basis to claim that whites used pot as much as blacks and Latinos, and accused the New York Civil Liberties Union, which had issued a report on the subject, of smearing the department while acting as a front for a marijuana-legalization group. Taking care of little crimes, including pot possession, "helped drive crime down," Mr. Browne said. In 2009, John Feinblatt, a mayoral aide, said, "This continued focus on low-level offending has been part of the city's effective crime-reduction strategy, which has resulted in a 35 percent decrease in crime since 2001." Last year, another aide, Frank Barry, said, "Marijuana arrests can be an effective tool for suppressing the expansion of street-level drug markets and the corresponding violence." At the state level, Mr. Cuomo won passage of legislation to expand collection of DNA to include people charged with misdemeanors. He agreed, in exchange for the support of Democrats in the Assembly, to exempt people facing a first arrest in minor marijuana cases. He also privately promised to fix a few lines in the laws governing marijuana possession, the changes he proposed this week. Currently, having a small quantity of pot is not a crime if it is not visible; it is merely a violation, like a traffic summons. However, if the pot is openly displayed, it is a misdemeanor. So, people ordered to turn out their pockets by a police officer are displaying marijuana, a misdemeanor. Those misdemeanor charges, Mr. Cuomo said, were an "aggravated complication" of searches conducted in New York City. Last year, about 700,000 people were stopped, questioned, and in many cases, searched; most of those people were black and Latino. Mr. Bloomberg and Mr. Kelly are under pressure over that practice, noted Donna Lieberman, the executive director of the New York Civil Liberties Union. A federal judge ruled last month that thousands of searches did not appear to be constitutional. The Legal Aid Society plans to sue the city over the marijuana arrests, said Steven Banks, the attorney in chief for the society, which provides many of the defense lawyers in New York's criminal courts. The main police union, the Patrolmen's Benevolent Association, has said there are quotas for the number of stops, although the Police Department calls them performance goals. Hakeem Jeffries, an assemblyman from Brooklyn, had urged the reforms proposed this week, which need the support of the State Senate to become law. "The possession of small quantities of marijuana is either a crime, or it's not," Mr. Jeffries said. It cannot be criminal behavior for one group of people and socially acceptable behavior for another group of people, where the dividing line is race.