The Washington area has maintained its position as the wealthiest large metropolitan area in the country even though income growth in the city itself has lagged substantially behind that in the suburbs, according to new 1980 census data released yesterday.

The median family income for the area was $27,515, the census reported, compared to $19,908 for all families nationwide.

Out of 38 metropolitan areas with population over 1 million, Washington ranked first, followed by San Jose, Calif., and the Nassau-Suffolk County area on Long Island, N.Y. The Washington area held the same top rank in the 1970 census.

However, despite such signs of economic vitality as the downtown construction boom and widespread renovation of old housing, median family income in the District of Columbia itself was $18,839, almost 32 percent below the areawide average and $1,069 below the nationwide median. In the 1970 census, D.C. lagged 27 percent behind the areawide average but was almost exactly at the national national family median of $9,586.

The new summary of census data also shows that the Washington metropolitan area has an exceptionally high number of high school and college graduates and a very high proportion of working women. At the same time, its proportion of one-parent families and persons living alone also is far higher than average.

Overall, the summary indicates that the Washington area took part in most of the major population and economic trends of the 1970s -- slower population increases, modest economic growth when inflation is accounted for, and sweeping changes in family composition and the role of women in the labor force.

In some respects -- small families, broken homes, and working women -- the area started ahead of the rest of the country in 1970 and was farther ahead when the decade ended.

Through it all, the Washington area slightly improved its economic edge, with its median family income winding up 38 percent above the country as a whole, compared to 35 percent ahead 10 years earlier. In the past two years since the census data was collected, the economy here has slumped considerably, though this too is part of a national trend.

The new census figures are provisional data based on a sample of 1.5 percent of the national population. Final data, expected to be issued over the next two years, will be based on about 20 percent of the nation's households.

According to the official Census Bureau definition, the Washington metropolitan area now includes the District of Columbia, its adjoining Mayland and Virginia jurisdictions, plus Charles County, Md., and Loudoun and Prince William counties and Manassas and Manassas Park in Virginia. All the income data are for 1979, the most recent year available when the census was taken on April 1, 1980. The median figures in which it is reported show the point at which half the families earned more and half earned less.

For white families in the area, the new census median is $31,004. For blacks, it is $19,329. However, black family income here is 53 percent above the median for blacks nationwide, a greater margin than the 49 percent advantage that whites in the area have over whites throughout the country.

The widening income gap between the District of Columbia and its suburbs probably is accounted for by the suburban migration of middle-class blacks.

Whites in the city generally are an affluent group, with a $33,848 median family income, but they make up such a small share of the city's population -- 27 percent -- that they cannot offset the relative poverty of blacks in calculating the citywide totals. The median income of D.C. blacks was $16,294 in 1979, though that still is well ahead of the $12,618 median for all black families in the United States.

Overall, the percentage of D. C. residents living in poverty rose from 17 percent in 1970 to 18.9 percent in 1980, although the actual number of poor people in the city fell by 6.6 percent. This results from the fact that the percentage of nonpoor city residents dropped by 17.5 percent as the city's total population fell by 16 percent to 637,651. At the same time, the percentage of people living in poverty in the area fell slightly from 8.3 to 8.2 percent, and nationwide from 13.7 to 12.5 percent. The poverty line for the 1980 census was $7,400 for a family of four.

In the suburbs, population growth overall was 12.6 percent, giving the area a total increase of 5.2 percent to 3.1 million, compared with an 11.1 percent increase nationwide.

The report also showed:

* The number of women in the area work force rose 48 percent, from 519,033 in 1970 to 767,901 in 1980. The nationwide increase was 46 percent.

* The number of high school graduates over 25 in the area was 79.9 percent, compared with 66.3 percent nationally. About 32.5 percent of area residents have four or more years of college, about double the national figure.

* About 23 percent of area families with children under 18 and 19 percent nationally have only one parent in the home, increases of 64 and 61 percent respectively.

* The number of persons in the area who live alone also rose sharply, from 209,400 to 285,823, and now account for 25.6 percent of all households here. The national figure is 22.7 percent.