NEW YORK — Police officers around the country have been able to protect themselves against citizen complaints by wearing tiny body cameras, but a federal judge’s plan to force some New York officers to start wearing the devices has angered the city’s mayor and police unions.

Mayor Michael Bloomberg criticized the cameras unnecessary for the 35,000-officer department, while police reform advocates have cautiously agreed to the idea in theory — with some caveats. And people on both sides have raised privacy concerns in a city that already has thousands of public and private cameras recording people.

“It needs to be examined further, which is why a test program is the right idea,” said Baher Azmy, legal director of the civil liberties group Center for Constitutional Rights.

U.S. District Judge Shira Scheindlin ordered a pilot program of the cameras and other major reforms to the New York Police Department’s stop-and-frisk policy this week, after she found the NYPD intentionally discriminated against minorities.

Bloomberg called the cameras no real solution and vowed to appeal, which likely means no changes are imminent.

“It would be a nightmare,” he said. “Cameras don’t exactly work that way. Camera on the lapel or the hat of the police officer — he’s turned the right way, he didn’t turn the right way, ‘my God, he deliberately did it.'”

There have been nearly 5 million stops in the past decade, mostly black and Hispanic men. About half the people who are stopped are subject only to questioning; others have a bag or backpack searched, and sometimes police conduct a full pat-down.

Only 10 percent of the stops result in an arrest; a weapon is recovered only a fraction of the time. A discrimination lawsuit filed in 2004 by four men, all minorities, became a class-action case, and Scheindlin presided over a 10-week bench trial this year.

The idea for body cameras came up almost by accident during testimony, when the city’s own policing expert raised it as something other cities use to determine whether police interact properly with the public. The judge seized on it.

“It would solve a lot of problems,” she said during trial. “Everybody would know exactly what occurred. It would be easy to review it. The officer would be aware he’s on tape.”

A yearlong pilot program in Rialto, Calif., ended in February, and researchers there found the number of use-of-force incidents dropped by half. The city of about 100,000 also had significantly fewer public complaints about police, dropping from 28 to just three.

In Arizona, Scottsdale police began using 10 body cameras about two months ago as the agency looks into equipping all of its roughly 250 patrol officers with the devices.

“We’re always being photographed out there, videoed by cellphone cameras, and we’d prefer, if possible, to have our own video of what happened,” Sgt. Mark Clark said.

Some officers were initially reluctant to use the cameras, Clark said, but an incident a few weeks ago changed several minds. Cameras revealed that a person who filed a complaint against a motorcycle patrol officer made up the story.

“We showed the person the video and they said, ‘Um, I guess I must have remembered it wrong,'” Clark said.

Phoenix police also are testing out the cameras with about 50 of its roughly 1,400 patrol officers as part of a study with Arizona State University.

“We want to know how it affects an officer’s job,” Sgt. Tommy Thompson said. “Are there people who will say, ‘Listen, turn off that camera or I’m not going to talk to you?’ When people are being filmed, do they calm down?”

An officer was fired last month when investigators reviewed video from his body-mounted camera and found he was profane and abrasive during calls and traffic stops, calling one person “an idiot.”

Las Vegas police are also testing a program to deploy cameras after the idea was endorsed by brass last year amid calls for a civil rights probe into the frequency of officer-involved shootings.

In New York, Scheindlin ordered one police precinct per borough where the most stops occur to host the yearlong pilot program. That means possibly more than a thousand officers would be recording with cameras on their eye glasses or lapels.

A court-appointed monitor tasked with overseeing all changes to the stop-and-frisk tactic must also iron out the details surrounding the cameras.

Among the questions: How much will this cost? The lapel units, about the size of a cigarette pack, range in price from $125 to more than $300 each. What is involved in creating virtual storage for the recordings? And most vexing for privacy advocates, how long would images be kept?

Patrick Lynch, president of the Patrolmen’s Benevolent Association, which represents rank-and-file officers, noted that the body cameras might be an extra burden and a redundancy.

“New York City is already saturated with video cameras,” Lynch said. “Our members are already weighed down with equipment like escape hoods, mace, flashlights, memo books, (expandable police batons) radio, handcuffs and the like. Additional equipment becomes an encumbrance and a safety issue.”

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Associated Press writers Brian Skoloff in Phoenix, Ken Ritter in Las Vegas and Jonathan Lemire in New York contributed to this report.