The rules regarding what officers record, and when, and who outside the department will have access to the footage, have yet to be made final.

A member of the City Council’s Public Safety Committee, Ritchie Torres, a Bronx Democrat, said he believed the “glacial pace” reflected a lack of enthusiasm. “What do you expect to happen when the N.Y.P.D. sets the terms and the pace of police reform?” Councilman Torres said in an interview. “I have trouble imagining it’s for lack of capacity,” he said of the delays. “I suspect it’s for lack of will.”

The mayor said the department has been acting prudently. “We’ve been very, very clear about the complication and the challenges of doing this in the biggest city in the country with the biggest police force, by far, in the country,” Mr. de Blasio, a Democrat, said at the news conference. “So we’re going be purposeful about getting it right. Once we start down the road, we have to make sure that we are getting it right.”

The timetable puts the New York agency behind a number of other big city departments.

The Chicago Police Department has 2,000 body cameras in use. The Los Angeles Police Department has so far deployed 1,160. In Charlotte, most of the police force is outfitted with body cameras.

In New Jersey, the State Police have a pilot program involving more than a 100 cameras, though many troopers also have a dashboard camera in their cars. The Newark Police Department, which was placed under federal supervision earlier this year after a Justice Department investigation, is not using body-worn cameras.

New York City and New York State have been slower than many jurisdictions in putting in place not only the use of body cameras but also some other criminal justice reforms.

And when it comes to transparency regarding officer misconduct, New York City is becoming more secretive. The city has filed a legal appeal to prevent the release of a summary of disciplinary records involving Daniel Pantaleo, the Staten Island officer who applied the fatal chokehold to Mr. Garner in 2014. This year it stopped providing reporters with notification of suspensions and other significant disciplinary actions against officers.