About 23 million Americans age 5 or over speak a foreign language at home, most of them Spanish.

One of every 8 Americans is poor.

There are 5.8 million single-parent families in the United States, and 18.2 million people living alone. But three-quarters of all Americans still live in "mom-and-pop" households.

Two-thirds of American workers drive to work alone in their cars every day, and the number of people using public transportation has dropped to 1 in 16 despite two fuel-short periods since the last census, when the figure was 1 in 12.

The number of mobile homes and trailers has skyrocketed.

These are among the provisional findings of the April 1, 1980, decennial census, showing the United States as a land of massive diversity, high living standards and educational attainments but slow economic growth since 1970.

The findings were released by the Census Bureau yesterday in its first big report on the social and economic characteristics of Americans in the 50 states and the District of Columbia.

The census found that the total population of the nation was 226.5 million (up from 203 million in 1970), of whom 189 million were white, 26.5 million black, and 3.7 million of Asian and Pacific Island derivation. The category of "other," including Eskimo, Indian and Aleut, accounted for 7.2 million people. Persons of Hispanic origin, regardless of race, totaled 14.6 million. Females totaled 116.5 million.

There were about 80.4 million households in the United States in 1980, 18.2 million of them composed of single people living alone. Another 3.3 million households were made up of unrelated people living together. The growth of these non-family households over the decade 1970 to 1980 was huge--72 percent--but there were still 48.6 million married-couple families (including remarriages).

And while there were 5.8 million single-parent families (19 percent of all families with children under 18, a big increase over 1970), about 74 percent of all the people in the United States lived in households headed by a married couple.

The District of Columbia had an unusually high percent of female-headed single-parent families: 28,369 out of the total of 63,403 families with children under 18. For Maryland, the figure was 105,569 of 573,598, and for Virginia, 118,289 out of 718,673.

Of the total U.S. population, 14 million were foreign-born, compared to 9.6 million in 1970. Some 23 million people aged 5 or older spoke a foreign language at home. For 48 percent of those people, the language spoken at home was Spanish.

About 62.3 million working Americans normally drove to work each day alone, while another 19 million car-pooled. Only 6 million used public transportion, a rate of 6.4 percent and a drop in the 1970 rate of 8.9 percent. (The rest walked or worked at home.) The New York metropolitan area (including surrounding towns and suburbs) had the highest rate of public transport use, 43 percent. Other high users were the metropolitan areas (including surrounding suburbs) of Chicago (18 percent), San Francisco-Oakland (17 percent), Washington, D.C. (16 percent) and Boston (16 percent), all having subways or surface-rail systems.

For the first time in history, every state had a high-school completion rate of better than 50 percent for persons 25 and over. The national average was 66.3 percent, compared with 52.3 percent a decade ago. Persons of Asian ancestry led in the rate of high school graduates at 74 percent. For whites the figure was 69 percent, for blacks 51 percent and for Hispanics 43 percent.

The District of Columbia figure was 68 percent, Maryland's 66.7 percent and Virginia's 62.5 percent.

College graduates totaled 17 percent, compared with 11 percent a decade ago.

There were 104.5 million people in the civilian labor force in 1980, compared with 80 million in 1970, and 44.6 million of them were women--a 46 percent increase over the decade. The number of men in the work force increased about 20 percent, to 59.9 million. Nearly half of women with children under the age of 6 were working.

About 1 in 8 Americans--12.5 percent--lived in poverty, based on income in calendar year 1979. (The poverty figure was $7,400 for a family of four). The number of Americans living in poverty a decade earlier was 13.7 percent. For whites the figure was 9.4 percent, for blacks 30.2 percent, for Hispanics 23.8 percent and those of Asian-Pacific ancestry 13.9 percent.

Among large metropolitan areas (city plus suburbs), the highest poverty rate was New Orleans (18.7 percent), while New York's Nassau and Suffolk counties had the lowest rate, 5.5 percent. For the District of Columbia metro area the figure was 8.2 percent, but the District alone had 18.9 percent without counting the richer suburbs that raise the average. Mississippi had the highest state poverty rate, 24.5 percent.

Median household income was $16,830, almost double the figure for a decade earlier, but after adjustment for inflation it was virtually the same as a decade earlier. However, adjusting for changes in household size, per capita income after inflation rose 18 percent to $7,313. Median family income was $19,908. For Asian-Pacific families it was $22,075, for whites $20,840, for Hispanics $14,711 and for blacks $12,618.

There were 51.8 million owner-occupied housing units and 28.6 million renter-occupied units in 1980. Only 2.9 million year-round units lacked full bathrooms.

Some 23.6 million units had central air-conditioning--three times the 1970 figure--and 24 million had one or more room units. Occupied trailers and mobile homes leaped from 700,000 in 1960 to 2.1 million in 1970 to 3.8 million in 1980. About 74 million of the homes had telephones, and 70 million had at least one car or truck (about three-fifths of these had more than one). About two-thirds of all owner-occupied homes on plots of under 10 acres had a mortgage, and the median monthly cost for mortgaged homes was $365, compared with $172 a decade earlier. For rental units, median gross rent (including utilities) was $243 compared to $108 in 1970.