In the first 178 days of 2013, the city averaged less than a murder a day, the first time the police can recall that happening for any sustained period. The latest numbers were recorded through Thursday.

Police Commissioner Raymond W. Kelly attributed much of the drop to a new antigang strategy meant to suppress retaliatory violence among neighborhood gangs. Police officials also credited their efforts at identifying and monitoring abusive husbands whose behavior seemed poised to turn lethal.

The recent decrease in violence is all the more striking because last year the department recorded the fewest homicides since it began a reliable method of compiling crime statistics half a century ago. The police recorded 419 murders in 2012.

“By far, it was the lowest, and guess what?” Commissioner Kelly said Friday morning before going on to announce that the number of murders this year was running about 25 percent below even that record year.

“In my business, in our business, this is miraculous. These are lives that are being saved.”

The relationship between the drop in murders and the department’s controversial policy of stopping, questioning and sometimes frisking people on the street was hard to immediately divine.

On the one hand, Mayor Michael R. Bloomberg and Mr. Kelly have cited the declining murder rate as a vindication of their policing strategies, which rely heavily on the stop-and-frisk tactic.

On the other, stop-and-frisks have dropped off considerably in the last 15 months, suggesting that the drop in murders might have been a result of other factors.

In the first three months of 2012, police records indicate, there were 203,500 stops. But in the first three months of this year, the police recorded fewer than 100,000 stops.

Over the last two decades, the decline in murders in New York has been greater than in other parts of the country. (In the early 1990s, when Mr. Kelly spent a little more than a year as police commissioner, the first of his two stints in the job, the city was coping with about 2,000 murders annually.)

Mr. Kelly has long discounted much of the criticism of stop-and-frisk as coming from a small number of advocacy groups that he says are disconnected from the communities in the Bronx, north Brooklyn and parts of Queens, where his policing strategies have been focused.

But even as the police make further inroads in suppressing violence in East New York, Brooklyn, and South Jamaica, Queens, neighborhoods with an outsize share of violence, there is a sense of frustration among police officials that their results have not quelled such criticism.

Referring to the drop in crime, Mr. Kelly said on Thursday, “Some people apparently are not satisfied with that.”

His remarks came hours after the City Council passed two pieces of legislation, one that would put in place an inspector general to investigate the Police Department and another that would expand New Yorkers’ ability to sue over racial profiling by officers.

Noting how the latest reduction of violence coincided with a diminishing number of street stops, some civil rights lawyers have grown more vocal in questioning not only the legality but also the effectiveness of stop-and-frisk tactics.

But police commanders point to what they say is the long half-life of the deterrent effect of stop-and-frisk, saying that criminals may decide to leave their guns at home because they have been stopped in the past, even if the odds of a stop have decreased in recent months. And the police say the decrease in violence has most likely led to a corresponding decrease in suspicious behavior, which results in fewer stops.

“Stop-and-frisk, believe me, that is one aspect of what we do, we have a whole complex array of tactics and strategies that we use,” Mr. Kelly said on Friday as he cited his year-old antigang initiative.

The program relies heavily on tracking the online activities of neighborhood gangs, in effect, trying to prevent shootings before they happen.

Mr. Kelly said that the initiative had led to a 52 percent decline in shootings in the 75th Precinct, which covers East New York.