For the first time since World War II the black population of the nation's cities has not grown, the U.S. Census Bureau reported yesterday.

"This marks at least a temporary end to the pronounced growth of the black population in cities that had characterized the past several decades," the bureau said.

Demographer Mark S. Littman, who wrote the report, said that "the rate of black growth in cities had been slowing for some time, and since the mid-1970s, the size of the black population in cities appears at a standstill."

Larry Long, chief of the bureau's population analysis staff, said the figures reflect "the fact that fewer blacks are leaving the South to go to northern cities, more are returning to the South, and blacks are moving to suburbs at an increased rate."

A comparison of black population growth in central cities over the decades -- while inexact because the number of such cities keeps increasing as population rises -- shows a stunning decline.

According to John F. Long, chief of the population projections branch, black population in central cities -- those with at least 50,000 people in metropolitan areas -- grew 48 percent in the 1940s, 50 percent in the 1950s and 35 percent in the 1960s.

But between 1970 and 1977 it grew only 4.2 percent, according to the new report, entitled "Social and Economic Characteristics of the Metropolitan and Nonmetropolitan Population: 1977 and 1970."

In 1970 about 12.9 million blacks lived in central cities. By 1974 that figure had grown to 13.7 million, but by 1977 it was 13.45 million, Littman said.

"The decline is not statistically significant because we're dealing with a sample rather than an exact count," he said. "But at least it shows there's been no change, and that's significant."

Black migration to suburbs appears to be accelerating, the report said.

"Between 1975 and 1977 black movement to suburbs accounted for 14 percent of the net increase in suburban population attributable to migration, compared with only 7 percent in the 1970-75 period," the study said.

"Although the number of blacks living in suburbs increased by 34 percent between 1970 and 1977, suburban blacks represent only 25 percent of the black metropolitan population and only 6 percent of the nation's suburban population," it added.

The bureau did not detail where the suburban migration of blacks is occurring, but a report by demographers Eunice S. and George Grier last April showed that much of the increase is in the Washington suburbs. Other significant black growth took place in the suburbs of Atlanta, Los Angeles and Philadelphia, their study indicated.

A District of Columbia government study last month showed that the city's black population was 519,200 last year, down 19,600 from 1976, and that its white population was 172,300, up 3,200 from 1976.

The census report showed that 55 percent of the nation's 24.5 million blacks lived in central cities in 1977, compared with 58.5 percent in 1970.

Demographers at the bureau declined to predict whether black population in cities would remain static or decline.

"There's a real difference of opinion on what city populations are going to be like in the 1980s," said Larry Long. "Everybody went wrong in the early 1970s when the nation's nonmetropolitan population began to grow and metroplitan population declined. Nobody had expected it."

The new study said net migration from metropolitan areas to rural areas and small towns was continuing into the latter half of the decade. It totaled about 600,000 between 1975 and 1977, the report said.

Because of migration, central cities lost a net of 10.5 million people and the suburbs gained a net of 8.2 million, it said.

White population declined 8 percent in cities but grew 10 percent in suburbs during the decade.

"However, this loss has been confined, since 1974, to central cities of large metropolitan areas," the report said. "The white population of central cities in smaller netropolitan areas (under 1 million population), while declining about 3 percent between 1970 and 1974, has showed no change since that time."

The report contained one set of figures that is bad news for cities: average family income of families moving out of cities was $16,000 in 1976; it was $15,000 for those moving in. The aggregate loss of income to people in cities was $18 billion, the report said.

The study also tended to undermine some popular myths -- that suburban men are largely white-collar workers (47 percent are, compared with 44 percent of city men who are); that suburban women stay home more than city women do (50 percent of suburban women and 48 percent of city women are in the labor force), and that suburbanites are far more family-oriented (43 percent of them have no children under 18 living at home; in cities the figure is 46 percent).