American blacks made major gains in education, home ownership and health during the 1970s, but unemployment worsened and the number of children living in one-parent families jumped enormously, the Census Bureau reported yesterday.

In a special analysis, the bureau gave a statistical snapshot of the nation's black population, which in the 1980 census numbered 26.5 million (12 percent of the population), together with some comparisons of where things stood at the start of the 1980s compared with a decade earlier.

It concluded that while there had been impressive gains in the status of blacks in some areas, the generally sluggish state of the economy since the economic downturn of 1974 had heavy impact on blacks and blocked rapid overall economic and social improvement.

Education was clearly one of the bright spots, according to the census study. Between 1970 and 1982, the proportion of blacks aged 25 to 34 who were high-school graduates almost caught up with that of whites. The proportion of whites who were graduates jumped from 76 to 87 percent, but the black gain was much more impressive, from 53 to 79 percent.

In higher education, there were also gains. The proportion of blacks aged 18 to 34 enrolled in college jumped from 7 to 11 percent from 1970 to 1981.

In 1970 only 15 percent of blacks aged 25 to 34 had completed one year of college, compared with 31 percent of whites. By 1982, the proportion of blacks had risen to 36 percent compared with 46 percent for whites.

The number of black homeowners also rose over the decade, jumping from 2.6 million to 3.7 million, a 45 percent increase, compared with a 26 percent increase for whites.

And blacks also showed some health gains, the study said. Black male life expectancy averaged 66 years in 1981, and females 75 years, double the rates of the early 1900s, although white life expectancies are still higher, 71 for males and 79 for females.

In economic matters, blacks did not fare so well. In 1972, the report said, the unemployment rate for blacks was 10.3 percent but 5 percent for whites, but by 1982, in the midst of the worst post-World War II recession, the black rate was 18.9 percent compared with 8.6 percent for whites.

The higher unemployment rate and other factors left 34 percent of all blacks below the government's official poverty line in 1981 ($9,287 for a family of four), the same proportion as in 1970. Whites increased from 10 to 11 percent over the same period.

As for income, census figures not included in the study but published elsewhere show that, measured in constant 1981 dollars, per capita income of American blacks rose from $4,378 to $5,129 from 1970 to 1981, a one-sixth increase in real income.

Income for black married-couple families rose from $18,370 in 1971 to $19,620, the study released yesterday said.

But while there were rises overall in per capita income and in the income of married-couple families, there was a large increase in the number of female-headed families with no husband present, from 28 percent in 1970 to 41 percent in 1982 (the figure for whites went up from 9 to 12 percent over the same period).

For black families of this category, real income measured in constant 1981 dollars declined, from $8,185 in 1971 to $7,510 in 1981.

What this means is that even though the overall individual average may have gone up because of gains by better-off and moderate-income blacks, for a large number of black families there was less cash income in 1981 than in 1971. (These figures do not take into account the value of food stamps or government medical benefits.)

The increase in the number of families headed by women was a major social phenomenon during the 1970s and the causes of it are not fully clear.

One result has been a large increase in the number of children living with their mothers with no father present, a situation that usually leads to economic difficulties.

In 1960, about a quarter of black children lived in one-parent households, according to Census Bureau figures published elsewhere. By 1970, the figure was 32 percent, and by 1982, 49 percent. The comparable figure for whites is 17 percent in 1982.

Here are other findings in the Census Bureau report:

Blacks in 1980 constituted a fifth or more of the population in seven states: Mississippi (35 percent), South Carolina (30 percent), Louisiana (29 percent), Georgia (27 percent), Alabama (26 percent), Maryland (23 percent) and North Carolina (22 percent).

Among cities, New York had the largest black population, 1.8 million, followed by Chicago, 1.2 million; Detroit, 758,000; Philadelphia, 638,000, and Los Angeles, 505,000.

Only 13 percent of blacks held managerial and professional jobs, compared with 22 percent for the work force as a whole.

In 1982 the divorce rate for blacks was 220 per 1,000 married persons living with their spouses, double the rate for whites and substantially higher than a decade earlier.

Some 55 percent of births to black women were out of wedlock, up from 38 percent in 1970. The 1980 rate for white women was 11 percent.