New York City Police Commissioner William Bratton sought on Friday to counter fears that lawlessness is on the rise in the largest U.S. city, writing in his resignation letter that crime has continued to fall this year.

The 68-year-old Bratton, a champion of the "broken windows" policing strategy that emphasizes pursuit of crimes no matter how minor, steps down on Sunday after four decades in law enforcement. He is to join the public relations and consulting firm Teneo.

Chief James O'Neill, the department's top uniformed officer, will succeed Bratton as commissioner.

In his letter to Mayor Bill de Blasio, Bratton wrote that an index of major crime in New York City dropped 5.7 percent during the two years after the mayor took office in 2014, and has fallen 2.5 percent so far this year.

The index includes serious offenses such as murder, rape and robbery, but not transit crime or minor larcenies or assaults.

Bratton attributed the decline to additional police officers and an emphasis on building bonds within neighborhoods.

De Blasio, a Democrat, campaigned in 2013 on ending the New York Police Department's aggressive "stop-and-frisk" tactic, which was used extensively under his predecessor, former Mayor Michael Bloomberg. The tactic, in which police can stop an individual on suspicion that a crime has been or is about to be committed and lightly search for a weapon, was reviled by civil rights leaders as disproportionately falling on minority residents.

Bratton also served as New York's police commissioner from 1994 to 1996 under Republican Mayor Rudy Giuliani.

Bratton is scheduled to be leave police headquarters with a ceremony at 3 p.m.on Friday.

(Reporting by David Ingram; Editing by Dan Grebler)