As murders in New York City have declined significantly over the last 25 years, one category has remained stubbornly high: domestic violence homicides.

The persistence of such killings, now a larger share of the shrinking homicide total, has frustrated police officers, prosecutors, social service providers and policy makers struggling to prevent intimate tensions that play out behind closed doors from turning deadly.

And while the city already has a host of programs aimed at curbing domestic violence, Mayor Bill de Blasio, a Democrat, announced this month that he was assembling a task force, headed by the first lady, Chirlane McCray, and James P. O’Neill, the commissioner of the New York Police Department, to come up with a “comprehensive citywide strategy” in the next four months.

The panel’s mandate is to find ways for social workers to intervene in troubled families before violence escalates, and to ensure more abusers are held accountable in court for their acts, aides to Mr. de Blasio said.