Serious crime in Northern Virginia declined in 1976, caused at least in part, area police say, by heavy emphasis on crime prevention measures.

The decline, part of a metropolitan-area trend, was reflected hjin the latest figures released by police which are based on the number of crimes reported in the FBI's seven major crimes index for January through December of 1976.

Based on the total number of crimes reported, Falls Church showed the largest decrease in the Northern Virginia area, a drop of 18.3 per cent from 1975. Fairfax City's crime rate was next, down 17.3 per cent. The crime rate in the three other jurisdictions also declined: Arlington dipped 10.3 per cent; Fairfax County was down 5.4 per cent and Alexandria, 4.9 per cent. (See box on page 9 for complete figures.)

Col. Kenneth Wilson, deputy chief of the Fairfax County police, said he believed the declining crime rate "came about as a result of the continuation of our crime prevention programs." Over the past year, he said, Fairfax County had also streamlined its services, which allowed the department to put more men on the street, increasing the police visibility in the community. Fairfax County, like other jurisdictions, has also concentrated on citizen involvement in crime prevention by teaching businessmen and homeowners about the most effective type of locks and the need to report suspicious behavior.

In Fairfax County, there were 23,194 serious crimes reported in 1976, down 1,323 from 1975. Of those, Fairfax police solved 11.2 per cent - a somewhat lower rate than 1975 with 12.6 per cent.

There was a drop in all categories of serious crime except aggravated assault, which increased 24.3 per cent over 1975. "Aggravated assault is like homocide," a Fairfax police spokesman said. "It's very, very difficult to prevent because the people involved usually know each other."

In Arlington, police reported a total number of 8,512 serious crimes in 1976, down 980 from 1975.The largest decrease occurred in the rape category with 34 in 1976, 19 less than '75, or a drop of 35.9 per cent. There were five murders reported, two less than the previous year, a drop of 28.5 per cent.

Capt. Alvin Fuschman, in charge of services for the Arlington department, explained the declining crime rate "as part of a national trend downward. The mood of the country seems to be changing. Also the general population is maturing. The war babies are growing up, getting married and settling down."

Capt. William A. Allen, chief of Arlington's criminal investigations division, said that although the police are stressing prevention and concentrated efforts on a particular crime, like robbery, "I would hate to point to something that we're doing here as having an impact. It's part of a national trend, sometimes it goes up and sometimes it goes down. It's been at rock bottom for the past three years."

Allen said that the county has also lost 20,000 of its population in the past two years, which may account for some decrease in the number of crimes.

The police in Arlington are continuing to ask citizens to report any suspicious incidents in their neighborhood, Allen said, "but people are little embarrassed to call the police. They're afraid that it won't be anything. We're trying to get people not to feel embarrassed, because those tips pay off."

Alexandria's total number of crimes reported in 1976 was down 481 with 9,306 in 1976 and 9,787 in 1975. There were 13 murders, one more than 1975 or an increase of 8.3 per cent. The number of rapes decreased drastically - 42 in 1976, 29 less than 1975, or 40.9 per cent.

Alexandria Police Chief John Holihan said he would not comment on the crime statistics, because "in my opinion we have nothing to do with it. I don't think we have the kind of knowledge that can tell why a man goes out and steals or commits a crime."

In Fairfax City, police reported there were 1,523 serious crimes in 1976, a drop of 319.

City Police Chief Leonard P. Kline attributed the downward trend to police prevention programs, including the home and business inspections program, and the creation of a block mother program that encourages citizens to report anything suspicious in their neighborhoods. Designated block mothers have been given the personal phone number of the police chief.

In Falls Church, there were a total of 810 serious crimes reported, 182 less than 1975. There were no murders; there was one murder reported in 1975. There were also no reported rapes; four occurred in 1975.

Tom Anderson, planner-analyst for Falls Church, said that the police had initiated several programs which may have had an impact on crime in the town and a citizens band group of volunteers, called PEEP, which helped patrol the city.

"We only have 24 patrol officers," Anderson said, "but they do a pretty good job. Their clearance rate (number of crimes solved) is between 23 and 25 per cent. Nationally, it's only about 16 to 18 per cent."