Amid criticism about the way New York City police officers enforce marijuana laws, Commissioner Raymond W. Kelly issued a memo to commanders this week reiterating that officers are not to arrest people who have small amounts of marijuana in their possession unless it is in public view.

The New York Legislature decriminalized possession of small amounts of marijuana in the 1970s, making possession of 25 grams or less a violation of the law that in most cases would not bring a jail sentence. But possessing even small amounts of marijuana in public view remains a misdemeanor.

Just over 50,000 people were arrested on marijuana possession charges last year, a vast majority of them members of minorities and male. Critics say that as part of the Police Department’s stop-and-frisk policy, officers routinely tell suspects to empty their pockets and then, if marijuana is displayed, arrest them for having the drugs in public view, thereby pushing thousands of people toward criminality and into criminal justice system.

Critics said the commissioner’s memo, reported on Friday by WNYC, represented a major change of policy. “This will make a tremendous difference because tens of thousands of young people — predominately young people of color — will not be run through the system as criminals,” said Steven Banks, the attorney in chief at the Legal Aid Society, which has handled thousands of the cases.