The number of serious crimes in the District of Columbia declined by 3.3 percent last year, the first decrease since 1976, Police Chief Maurice T. Turner Jr. announced yesterday.

The District's report made it unanimous throughout the Washington area: crime declined in 1982 in every major jurisdiction compared to the previous year, with the number of burglaries having dropped the most.

The number of crimes dropped by 11.2 percent in Montgomery County, 9.5 percent in Prince George's County, 10.4 percent in Anne Arundel County, 17 percent in Arlington County, 11.6 percent in Fairfax County, 14.6 percent in Prince William County, 27 percent in Fairfax City and 6.2 percent in Alexandria. Such figures are a local reflection of the nationwide drop in crime.

In addition to the 12 percent decline in burglaries, which dropped from 16,832 in 1981 to 14,774 last year, the D.C. statistics showed that the number of slayings dropped from 223 in 1981 to 194 last year, while the number of robberies went from 10,399 to 9,137. However, of the remainder of the seven major crimes reported to the FBI, four categories of crime increased: car thefts from 3,765 to 4,086, aggravated assaults from 3,432 to 3,645, rapes from 336 to 353 and larcenies from 32,845 to 33,435.

In the District last year, there were 65,692 major crimes reported, more than 26,000 higher than in Prince George's County, which had the second largest total. The number of D.C. crimes had been rising steadily each year since 1976, when the total was 49,726.

But Turner said the city's 1982 reduction--a drop of 2,218 reported offenses from the 1981 figure of 67,910--marked a turning point in his department's effort to curb crime. The chief said his goal is to curb crime 12 percent more this year.

Turner, echoing previous assessments by police officials in suburban jurisdictions, said the number of crimes was reduced last year through increased community cooperation in fighting crime, such as the use of antiburglary Neighborhood Watch programs, a variety of police operations that have targeted specific types of crimes and the jailing of more offenders, particularly repeat offenders. He said the District's prison population increased by 700 last year, to a total of 2,200.

"We made citizens aware" of the need to report crimes, "to become our eyes and ears," Turner said of the Neighborhood Watch programs in which citizen patrols radio for police when they spot possible crimes.

Turner said that since 1981, a D.C. police narcotics task force has made 4,500 arrests, while other police in the last two weeks recovered $300,000 worth of stolen property by focusing on local fencing operations.

He said the police effort against fencing is continuing. "Most stolen property is purchased by law-abiding citizens," Turner noted. "We want them to know that's a crime."

Turner said that crime was reduced in all seven police districts during the last three months of 1982, compared to the same period in 1981. For the year, crime increased in three of the districts: the 2nd (2 percent), which includes Georgetown and most of downtown; the 3rd (1 percent), which includes Shaw and the 14th Street NW corridor, and the 5th (0.7 percent), which includes LeDroit Park and near Northeast Washington. Crime dropped by 12 percent in the 1st Police District, which includes Capitol Hill and Southwest Washington, and by 4 percent in the 4th, the Georgia Avenue NW corridor; the 6th, far Northeast and part of Southeast, and the 7th, the rest of Southeast.

There were 39,101 reported crimes in Prince George's last year, 26,248 in Montgomery, 14,011 in Anne Arundel, 23,600 in Fairfax County, 7,905 in Arlington, 8,550 in Alexandria, and 5,311 in Prince William, according to local police departments.

Washington Post staff writer Alfred E. Lewis contributed to this story.