“It’s too early to call this an end to the crime drop, but we are facing a one-year rise in murders that is quite substantial — the largest in about half a century,” said Richard Rosenfeld, a criminology professor at the University of Missouri-St. Louis, and an authority on crime trends.

“Alarm is not the appropriate response,” he said, “but the priority should be in improving police-community relations, particularly in disadvantaged African-American communities.”

The data was released on a day when a gunman in Houston wounded nine people before being fatally shot by the police, and in the midst of a heated presidential campaign in which the Republican candidate, Donald J. Trump, has made law and order a central tenet.

Saying that “crime is out of control, and rapidly getting worse,” Mr. Trump has pledged to make the country safe again. He suggested last week that stop-and-frisk policing, a tactic that has been ruled unconstitutional and subsequently discontinued in New York City, might be a model for other cities.

The Democratic candidate, Hillary Clinton, has called for an overhaul of the justice system and a rebuilding of trust between law enforcement officers and the communities they serve. She has also called for stricter gun control.