Falls Church has the second highest per capita income in the nation and four other Washington area jurisdictions rank among the top 15, according to 1979 income figures gathered for the 1980 census.

Falls Church's per capita income of $12,885 ranked behind only the Bristol Bay region of Alaska, with its income of $14,948, according to the Bureau of the Census report, which surveyed 3,137 counties, county equivalent areas or independent cities with populations of 100 or more.

Arlington County was fifth in the nation, with a per capita income of $12,565. Montgomery County ranked seventh, with $12,339. Alexandria was eighth, with $12,209, and Fairfax County was 11th, with $11,551.

Other area rankings included Fairfax City, 29th; the District of Columbia, 68th; Loudoun County, 75th; Prince George's County, 98th; Anne Arundel County, 124th; Prince William County, 153rd; and Charles County, 363rd.

Five regions in Alaska and the five jurisdictions in the Washington suburbs dominated the census list of the nation's highest incomes. Also included in the top 15 were the counties containing New York's prosperous Manhattan borough and Colorado's Aspen ski resort community. Also on the list were California's Marin County just north of San Francisco, the ski resort community of Alpine County, Calif., and Johnson County, Kan., a suburb of corporation-rich Kansas City, Mo.

Census officials said yesterday that changes in the income rankings, some of them dramatic shifts from a decade ago, often depended on the changing composition of the population for certain regions and on peculiar economic, geographic and political characteristics of communities.

Alaska, for example, has inflated salaries fueled by the oil boom to meet its high cost of living, and communities with large populations of single persons tend to have higher per capita incomes than regions populated mostly by families.

Falls Church Mayor Carol DeLong was skeptical that the survey's findings meant her community is a "rich town." She said the Falls Church mailing address covers much surrounding territory in affluent Fairfax County, creating possible confusion about its actual inhabitants. The region is heavily populated by mid-level federal employes and, because of an unusual Virginia law, is an independent city within the county.

Falls Church's per capita ranking increased from 1969, when it was listed fifth, and the jurisdictions of Alexandria and Fairfax County also climbed in their rankings, from 11th to eighth place, and from 14th to 11th place, respectively.

But Arlington County dropped from first place in 1969 to fifth place, and Montgomery County fell from third to seventh, although officials noted that the changes are negligible and do not indicate a declining economy. It may be, said one Arlington official who had not seen the survey, "that Arlington increased its per capita income a lot but maybe not as much as other areas."

Other Washington area jurisdictions which rose in the census rankings were Loudoun County, from 367th to 75th; Anne Arundel County, from 162nd to 124th; Prince William County, from 444th to 153rd; and Charles County, from 870th to 363rd.

The District fell from 50th place to 68th, while Prince George's County dropped from 63rd to 98th place. Fairfax City fell from 26th to 29th place.

The community with the lowest per capita income was Shannon County, S.D., with $2,637. Two other South Dakota communities, Buffalo County and Ziebach County, Texas' Starr County and Owsley County in Kentucky also were listed among the lowest in the nation.