Major crimes reported in Washington increased by 2 percent during the first seven months of this year compared to the same period last year, with the greatest rise occurring in auto thefts, rapes and larcenies, D.C. police announced yesterday.

The statistics showed 2,364 auto thefts in the first seven months of this year, up 14 percent from the same period last year; 243 rapes and attempted rapes, up 9 percent, and 2,041 aggravated assaults, an increase of 2 percent over last year.

However, some categories showed declines in the period under study. From January through July 8,759 burglaries were reported, down 8 percent over the same period last year; 5,202 robberies, down 5 percent, and 118 homicides, down 0.8 percent, according to statistics released yesterday.

Total larcenies reported were 19,253, up 8 percent over the first seven months of 1981. Of those larcenies, 10,058 were from cars, an increase of 19 percent in that category.

"Half of the crimes committed in the District were larcenies from autos," D.C. Police Chief Maurice Turner said. "We have to teach people how to protect their own property."

Mayor Marion Barry, who attended a press conference at which the statistices were released, said he plans to "tell citizens to take all of their valuables out of their cars and leave the doors unlocked." He said that practice would reduce the amount of damage done to a vehicle if someone tries to steal articles from it.

The statistics offered a glimpse at how individual areas of the city have fared in the war against crime during the past year. The only decline in overall crime occurred in the 1st District, which includes sections of downtown, Capitol Hill and Southwest. Though crime decreased 10 percent there, it rose 10 percent in the 3rd District, which covers most of the inner-city area of Northwest Washington, including the 14th Street strip and many major drug-trading areas.

In the 2nd District, crimes increased by 9 percent; in the 4th District, 1 percent; in the 5th, 6 percent; in the 6th, 0.8 percent, and in the 7th, 0.7 percent.

Although the total number of reported crimes climbed from 5,138 in June of this year to 5,799 in July, Turner noted that July's crimes were fewer than those reported in July of last year, and said he considers that a hopeful sign.

"I feel the tide is turning against crime and we are winning some of the battles against crime," he said. "We must however, continue to intensify our efforts and work toward the goal of putting criminals where they belong, behind bars."

He said he expects overall crime statistics for August, not yet officially released, to be lower than those of August of last year, and he said both the neighborhood watch program and the recently created repeat-offenders unit have helped fight serious crime.

Despite the increase from 37,249 reported crimes in the first seven months of 1981 to 37,980 in 1982, Barry echoed Turner's optimism.

"We're gaining. We've got the criminals on the run," Barry said. "They're not going to run us out of town; we're going to run them into job training programs . . . and if they don't want that, we're going to run them into jail."

Before releasing the new crime data, Barry and Turner unveiled new equipment for analyzing fingerprints, which Turner said would enable officers to determine quickly whether someone arrested for a minor offense was wanted for a more serious crime. The equipment, valued at $40,000, will initially be used only in the 3rd District.