When Mayor Bill de Blasio took office in January, community groups and juvenile justice advocates hoped that his administration would significantly decrease the numbers of black and Latino young people who are unfairly — and in some cases, illegally — arrested and dragged through the court system for possession of tiny amounts of marijuana. But a new analysis of state arrest data by a nonprofit called the Marijuana Arrest Research Project, which studies police policy, suggests that the de Blasio administration is on track to equal the more than 28,600 low-level marijuana arrests that were made under Michael Bloomberg in 2013. The administration needs to review Police Department policy to make sure these arrests are necessary and being fairly made.

The State Legislature tried to correct the problem in 1977, when it barred the police from arresting people for tiny amounts of marijuana unless the drug was publicly displayed. The number of minor arrests declined immediately after the law was passed but rose sharply from fewer than 1,000 in 1990 to 50,000 in 2011. Research has repeatedly shown that whites and minorities use the drug at similar rates, yet more than 80 percent of those arrested are black or Latino. And even though most cases are eventually dismissed, the arrests exact a cost: Young people who are even temporarily entangled in the courts can be shut out of jobs or denied entry into the armed services.

As the number of arrests skyrocketed, defense attorneys made the case that police officers were illegally charging suspects with “public possession” after directing them to reveal the drug or removing it from their pockets during constitutionally questionable searches. Police Commissioner Raymond Kelly tacitly acknowledged that problem in 2011, ordering officers to follow the 1977 law. The numbers of arrests declined significantly. The 28,600 arrests made last year may seem low compared with the number in 2011.

The police have historically implied that marijuana arrests help get criminals off the street. But a majority of these low-level arrests end in an “adjournment in contemplation of dismissal,” which means that the charges go away if the person stays out of trouble for six months or a year, or in a plea to a violation, which is a noncriminal disposition. (These cases waste scarce court resources and distract prosecutors from working on serious crime.) Moreover, a 2012 study by Human Rights Watch found that only about 3 percent of people arrested for low-level marijuana possession subsequently committed even one violent felony.