Thousands of people carrying small amounts of marijuana may no longer be arrested or face criminal charges, city officials announced Monday, marking a significant shift in how the nation's biggest city approaches policing pot.

Instead of being arrested on misdemeanor charges that carry potential punishments of up to three months in jail, many people will get court summonses and face non-criminal violations punishable by fines starting at $100, Mayor Bill de Blasio and Police Commissioner William Bratton said.

While state law makes it a misdemeanor to have up to 25 grams - about a sandwich bag - of marijuana in "public view," the mayor characterized stopping such arrests as an enforcement choice. He said it would give police officers time to pursue more serious crime and spare people from the consequences of arrest records for cases that often end up getting dismissed.

It's "a smart policy that keeps New Yorkers safe, but it is also a more fair policy," said de Blasio, a first-term Democrat who's faced pressure to keep campaign promises to reduce the more than 20,000 such arrests per year.

The announcement comes a week after voters in Washington, D.C., and in Oregon and Alaska approved measures legalizing marijuana, joining Colorado and Washington states. De Blasio and Bratton oppose legalizing the drug.

City lawmakers, district attorneys and civil rights advocates including the Rev. Al Sharpton hailed the change, and the police captains' union president noted it would eliminate cases that often get dismissed and subject officers to criticism. But the city's biggest police union said it could tie officers' hands.

"We do not want police officers left holding the bag if crime rises because of poor policy," Patrolmen's Benevolent Association President Patrick J. Lynch said in a statement. "Writing a summons to someone who does not respect the law can result in a volatile situation."

Under a 1977 state law, it's only a violation to have up to 25 grams of marijuana in a pocket or bag, but the offense rises to a misdemeanor if the pot is being smoked or is "open to public view."

Under the new policy, set to take effect Nov. 19, people caught smoking will still be arrested, as will people with open warrants or no identification. Prosecutors estimated it would affect 92 percent of the lowest-level marijuana cases in Queens and about 50 percent in Brooklyn, where the district attorney has taken his own steps to curtail pot prosecutions.

The arrests averaged about 2,100 a year citywide from 1978 through 1995 and then shot up, peaking at 50,700 in 2011. Amid scrutiny of police tactics and some policy changes, they fell to 28,600 last year. There have been 24,080 this year.

Critics say the arrests are racially disproportionate: Federal statistics show similar rates of marijuana usage among whites, blacks and Hispanics, but about 86 percent of the New York arrestees are black or Hispanic. Critics also say police illegally search people or get them to empty their pockets to bring the drug into the open and generate arrests, though officers were reminded in 2011 they couldn't do that.

"This proposal can only be considered a first step," said Gabriel Sayegh, a managing director of the Drug Policy Alliance, which advocates for less restrictive drug laws.

As the arrests persisted, Brooklyn DA Kenneth Thompson announced in July he would drop many of the cases before the defendants had to go to court. His office has dismissed about one-third of such cases. Under the city's new policy, those defendants will instead have to go to a crowded Manhattan summons court, he noted.

Some of his colleagues said the change would ease packed dockets in criminal courts, and Manhattan DA Cyrus R. Vance Jr. called it "the right thing to do."