The District has seen crime in some categories, including homicides and robberies, fall in 2011, Mayor Vincent C. Gray and Police Chief Cathy L. Lanier announced Wednesday.

Homicides are down 11 percent and robberies 7 percent through August 1, Lanier said.

In a joint press conference held at the Mary Virginia Merrick Center in Southeast, the chief said violent crime fell by an average of 37 percent in five specific neighborhoods that have historically had persistent crime problems.

Overall, however, statistics released Wednesday show that total crime in the District — which includes violent crime and property crime — was up by 3 percent through August.

Gray (D) attributed the decreases to a summer effort to partner city agencies to target such issues as abandoned cars, overgrown grass and youth crime.

Beginning in May, Gray said, he directed city agencies to work together so that quality-of-life issues — including dirty playgrounds, dark alleys, overgrown grass and weeds — were addressed “within hours.”

Additionally, he said, residents took part in programs including city-sponsored basketball and football games.

Gray said the city’s summer jobs program was also helpful in keeping youth safe this summer. Nobody under the age of 18 has been killed in the District since June 21, he said.

Gray said the collaborative strategy would continue year-round, and a report on the effectiveness of the summer effort would be released in the fall.