There are poor people in Fairfax County, but not many.

According to statistics collected in the 1980 Census and assembled by the Northern Virginia Planning District Commission, most Fairfax residents--525,000 out of 597,000--live at better than twice the poverty level. Only 6 percent of the homes in the county are without air conditioning. Sixty-two percent of the county's households have at least two cars, and 19 percent have more than two.

But if the census data confirm some common impressions of life in the wealthy suburb, they also help dissolve some myths. Although most Fairfax families still live in single-family, detached homes (58 percent of all occupied houses, trailers and apartments) and 87 percent of the families with children include two parents, the working and living patterns of the "Leave It to Beaver" era are no more, the census shows.

Many more women now work than do not work, for example. There are 141,000 Fairfax County females 16 years or older in the work force and 87,000 outside it. Sixty percent of the women with school-age children work, and just under half of the women with children 6 years old or younger are also in the labor force.

Nor is the county the bedroom suburb of Washington it once may have been. More than one-third of the workers who live in Fairfax also work in Fairfax, and fewer than one-fourth commute to the District itself.

That smaller proportion of Fairfax residents working in the District, along with Metro's limited availability to Virginia commuters, means that only 8 percent of the county's work force (24,000 people) uses public transportation. Another 25 percent (80,000) drives to work in car pools, but most of those have only two riders. Only about 7 percent of the work force, in fact, drives in the four-person car pools that qualify for access to the commuter lanes of I-66 and I-395, and the bulk of Fairfax's work force (192,000) still drives to work alone.

When they get to work, the most common occupations are clerical (64,000 people), followed closely by professional (63,000) and executive and managerial (60,000). Blue-collar workers (5,000) are at the bottom of the chart.

One-third of the Fairfax work force is employed by federal, state or county government.

Despite the controversy generated by the issue of saving farm land in the county, the census uncovered almost no one living on farms--205 people, compared with 437 in 1970. (About 1,800 residents of the county worked in farming, fishing or forestry, though not necessarily within Fairfax.) Another startling statistic explains where much of the farm land has gone: fully 42 percent of the county's households live in structures built since 1970.

Northern Virginia politicans often complain about the difficulties of campaigning when everyone moves so frequently, and the census supports the gripe. Only 37 percent of the county's residents were living in the house they occupied five years before. On the other hand, the county's residents are highly educated; 62 percent have been to college for at least one year.

Single men outnumber single women (64,900 to 55,800), but there are more women who are separated (7,000 women to 5,800 men), divorced (15,400 to 9,400) and widowed (14,900 to 2,400). Most families own their homes, but about one-third of the county's housing units are occupied by renters--and more than two-thirds of all black families live in rental units.

Blacks make up 6 percent of the population, and they are poorer on the average than any other group. Of the white majority in the county, 3 percent live below the poverty level as do 12 percent of the blacks, 9 percent of the Asians (among whom Koreans predominate) and 6 percent of the Hispanics. Altogether, 23,000 residents live below the poverty line.

Finally, there there may be a positive note for the Postal Service in Fairfax: 5,700 homes in the county still lack a telephone.