The plan, he said, is to have protests and antiterrorism duties handled by different types of officers, in different corners of the department.

A specially trained unit of 300 to 350 officers with heavier gear will be assigned to counterterrorism patrols currently performed by precinct officers who are temporarily detailed to high-risk areas of the city, like Times Square.

“It’s time to institutionalize, if you will, make permanent, that concept,” Mr. Bratton said, standing alongside many of his chiefs. That unit will augment the Emergency Services Unit, whose officers carry heavy weapons and whose Hercules teams are often seen at potential terrorism targets.

Separately, he said, the department would create a unit of roughly 500 patrol officers who would help with temporary issues, like a rise in crime in any precinct or large protests. Mr. Bratton said those officers would be known as the Strategic Response Group.

Mr. Bratton described the reorganization at a briefing with reporters that included topics such as a killing in Queens (a 50-year-old shot his friend visiting from Europe with an antique revolver, the police said); a Bronx drug seizure; and monthly statistics that showed an increase in murders and shootings. The number of crimes committed with guns is up across the city, he said, as are crimes committed by those recently released from jail.