Serious crime in Alexandria fell 6.2 percent in 1982 compared with the previous year, dropping to its lowest level in three years, city police said yesterday.

But officials at City Hall continued to express concern about the prevalence of violent crimes, while viewing the annual statistics as a welcome development.

Recently released crime statistics in neighboring suburban communities show that Alexandria is part of a regional, as well as national, trend. Crime fell 17 percent in Arlington and 11.6 percent in Fairfax County.

In Alexandria, the greatest percentage decrease in crime was reported in homicide, which dropped by 65 percent, from six deaths in 1982 compared to 17 the year before. City Council member Donald L. Casey (D) said those figures weren't "statistically significant" because the number of murders in Alexandria, whose population is almost 110,000, are so few.

"The six bother me just as much as the 17," council member Margaret B. Inman (R) said, adding that what most alarms her is that violent crime appears to be occurring more in highly populated areas and at all times of day.

Overall, there were 8,550 serious crimes in Alexandria in 1982 compared to 9,122 in 1981 and 8,251 in 1978, according to city police spokesman Sgt. Kathy Salvas.

Of the seven serious crime categories, police said three showed increases: robbery was up 6.8 percent at 591, aggravated assault was up 1.27 percent at 320 and motor vehicle theft was up 9.76 percent at 506. Burglaries were down 20 percent to 1,754, rapes declined by 3.13 percent to 62 and larceny went down 3.77 percent to 5,311.

Police Chief Charles T. Strobel attributed the decline to neighborhood watch programs, an increased awareness of crime prevention and a greater effort to curtail the activities of career criminals.