The gradual return of whites to Washington continued during 1977, new District government figures show, as the city's white population increased for the second year in a row after a steep decline that lasted for a quarter of a century.

At the same time, the number of blacks fell again as it has each year since 1972.

Overall, Washington was 75.1 percent black in 1977, according to the new population estimates. This was the highest proportion of blacks for any major city in the United States, although it is slightly less than the peak of 77.5 per cent black reached here in 1975.

"The white population has bottomed out and now is rising slightly," said Albert J. Mindlin, the city's chief statistician, whose office issued the new estimates. "The state of the art (in making racial estimates) is far from perfect, and the change is small, but we think it's happening."

According to the report, Washington had 172,300 whites in 1977, up 3,200 from a year earlier and almost 10,000 more than the low-point of 162,700 in 1975.

Most of the increase, the figures indicate, is among whites in their late 20s and 30s. Although no additional detailed data is available, Mindlin and other deomgraphers said many apparently are single adults and childless couples who have moved into rowhouses, formerly occupied by blacks, in inner-city neighborhoods such as Capitol Hill, Shaw, and east of Dupont Circle.

The changes in these areas have brought soaring real estate prices and elaborate restorations. They also have produced charges, strongly voiced during the city election campaign, that low-income blacks are being hurt by displacement.

Overall, Washington had 519,200 blacks in 1977, the city report said, down by 19,600 from a year earlier and 46,000 fewer than the peak reached in 1972.

The steepest decrease, the report indicated, was in black children under age 15, reflecting both a sharp drop in births and plummeting enrollment in D.C. public schools.

"It's mostly black families with kids who move to the suburbs in search of better schools," said George W. Grier, a demographer and urban planning consultant who has conducted several major studies of local population trends.

In a report issued last winter by the Washington Center for Metropolitan Studies, Grier and his wife Eunice concluded that most of the new black suburbanites are middle-income families with young children. They have higher levels of income and education, the Griers said, then the average for blacks remaining in Washington.

"The moves seem to be voluntary," George Grier said. He said there is no evidence that poor blacks leaving inner-city neighborhoods because of renovation are moving to the suburbs.

"It probably is a stepping process," Grier said, "where families move from an inner-city neighborhood to neighborhoods farther out, and two, three, or four steps removed somebody eventually moves to the suburbs. Those who do move out (of Washington) generally are stepping up to better housing."

Grier added that movement of blacks to the suburbs has been speeded by laws against housing discrimination and by rising black incomes, particularly for those with government jobs.

Another factor in the decline of the city's black population, Mindlin said, has been the end of out-migration from the South, which used to supply virtually all of Washington's black newcomers.

Both Grier and Mindlin said nationwide changes in family and work patterns, particularly the large increase in women holding professional jobs who delay having children or choose not to have them, may play an important part in the city's white population rise.

"The education factor, which used to drive a lot of (white) people to the suburbs, now doesn't operate," Mindlin said.

From 1950 to 1970 the city's white population fell from 517,865 to 209,272. The number of white children in public schools dropped from 46,221 to 7,555. The only white age group that increased slightly was the elderly.

Thus, by the early 1970s, Grier said, "there were very few white families with kids left, and more and more singles and childless couples who just don't think much about schools."

Those who do have children generally keep their families small, he said and in some cases with both husband and wife working they can afford private schools.

From 1975 to 1977, the number of whites enrolled in Washington's private schools increased by 771, to 7,531. The number of whites in D.C. public schools rose by only 49, to 6,152.

Grier said the increasing employment of women in high-level jobs has been a significant factor in whites choosing to live in the city.

"With a two-earner household the convenience of living close to your job becomes more important," he said. "They like to work, and if they have one kid, they like to get home quickly (to see the child)."

"There's a whole new class of people as far as their value system is concerned in relation to the city," Grier said. "And as the word gets around, more and more want to live there."

Mindlin said the white increase also probably reflects a lessening of prejudices against blacks. "These mostly are liberal whites living in inner-city neighborhoods," Mindlin said."They like city living. They enjoy the intercultural thing. They don't have the prejudices their parents had. A lot of them say they want to live near blacks."

To an important extent, Mindlin said, the increase in whites in the District is caused not by more whites moving into the city but by fewer whites leaving once they come here. Even in the 1950s and 1960s, when the overall white population plummeted, there was a substantial influx of whites in their early 20s. But almost all of them left in their late 20s and 30s as they established families.

"That's not happening so much any more," Mindlin said. "The whites who used to move to suburbs now are staying in the city."

He said this was shown clearly in recent studies of new homebuyers in Mount Pleasant and Capitol Hill. Very suburbs, he said, while the great majority were relatively young couples who had rented in the District before deciding to buy a house.

In 1970, the last year for which an official census is available, Washington had 547,238 blacks and 209,272 whites, for a black proportion of 72.3 percent. In the 1960 census blacks accounted for 54.8 percent of D.C. residents.

The new city estimates are based on birth, death, and school enrollment data, Mindlin said, and should be used cautiously.