More than 40 years after the federal government enacted fair-housing legislation and the Great Migration of blacks from the South began to ebb, residential segregation in metropolitan America has been significantly curtailed, according to a study released Monday.

The study of census results from thousands of neighborhoods by two economics professors who are fellows at the Manhattan Institute, a conservative research organization, found that the nation’s cities are more racially integrated than at any time since 1910; that all-white enclaves "are effectively extinct"; and that while black urban ghettos still exist, they are shriveling.

An influx of immigrants and the gentrification of black neighborhoods contributed to the change, the study said, but suburbanization by blacks was even more instrumental.

The progress was less pronounced between blacks and non-Hispanic whites, though, than it has been between blacks and nonblacks, including Asians and Hispanic people.

The findings by the two professors — Edward Glaeser of Harvard and Jacob L. Vigdor of Duke — were generally seconded by a spectrum of other experts with several caveats and an admonition that the study should not be seen as declaring the end of all segregation.

Also, barriers like exclusionary zoning in the suburbs persist, and the decline in busing to achieve racial integration means that some public schools are more segregated than before.

"There is now very much more black-white neighborhood integration than 40 years ago," said Professor Reynolds Farley of the University of Michigan’s Population Studies Center. "Those of us who worked on segregation in the 1960s never anticipated such declines. Nevertheless, blacks remain considerably more segregated from whites than do Hispanics or Asians."

Douglas Massey, a Princeton sociologist, said: "In terms of trends in black-white segregation, we really see two trends: In metro areas with small black populations, we indeed observed sharp decreases in segregation; but in those with large black populations, the declines are much slower and at times nonexistent. Although all white neighborhoods have largely disappeared, this is more due to the entry of Latinos and Asians into formerly all-white neighborhoods."

William H. Frey, the chief demographer at the Brookings Institution, cautioned that "the report sends a potentially harmful message that black-white residential separation is no longer a priority issue in this country."

"While recent modest declines in black segregation levels are welcome, the 2010 census shows that the average black resident still lives in a neighborhood that is 45 percent black and 36 percent white," he said. "At the same time, the average white lives in a neighborhood that is 78 percent white and 7 percent black. Black segregation levels are even higher for children, signaling the continued separation of black and white families across communities with different levels of resources available for schools and other services important for nurturing the next generation."

John R. Logan, a Brown sociologist, said: "If we want to understand the long-term trends in segregation, we have to be aware both of the progress and of the resistance to change. We are far from the ‘end of segregation."’

Still, Glaeser and Vigdor found that only 20 percent of blacks now live in "ghetto" neighborhoods where 80 percent of the population or more is black, compared with nearly 50 percent who lived in similar neighborhoods a half-century ago.

The findings in the report, titled "The End of the Segregated Century," for the Manhattan Institute’s Center for State and Local Leadership did not denigrate decades of desegregation efforts. In fact, the authors said, "there is every reason to relish the fact that there is more freedom in housing today than 50 years ago and to applaud those who fought to create the change." But they concluded that housing desegregation was not a magic bullet in providing equal opportunity.

"Residential segregation has declined pervasively, as ghettos depopulate and the nation’s population center shifts toward the less segregated Sun Belt," Glaeser and Vigdor wrote. "At the same time, there has been only limited progress in closing achievement and employment gaps between blacks and whites."

While the decline in New York and St. Louis was "not very profound," Vigdor said, new neighborhoods like the Washington Navy Yard in the District of Columbia shifted to 31 percent black in 2010 from 95 percent black in 2000. Nonetheless, 17 census tracts that encompassed 46,000 Washington residents and were more than 98 percent black in 2000 were still more than 95 percent black in 2010.

The study’s definition of neighborhood was borrowed from the census: a tract that is home to 1,500 to 7,500 people. The analysis relied on the two most common segregation indexes: dissimilarity, or the proportion of individuals of either group that would have to switch neighborhoods to achieve perfect integration; and isolation, which measures neighborhoods where the share of the population of one group surpasses the citywide average.

By those measures, the average black person still lives in metropolitan housing markets where to achieve complete integration more than half the black population would have to move and in neighborhoods where blacks exceed their share of the region’s population by about 30 percentage points.

Many of the cities with less segregation — or cities that demonstrated disproportionate gains in integration — are in the Sun Belt, where population growth has been greatest and immigrants have congregated. Those gains are attributable, in part, to the proliferation of subprime mortgages and are threatened by the foreclosure crisis.

By the dissimilarity index, Dallas and Houston are the least segregated big cities. Los Angeles fared best on the isolation index. Sun Belt cities accounted for fully half of the 10 metropolitan areas with the largest black populations in 2010, compared with only two in 1970. That helps explain why the dissimilarity index plunged nearly 40 points in metropolitan Dallas but less than 10 points (nearly half of that since 2000) in New York.

Among cities with the largest black population, Chicago, Cleveland, Detroit and St. Louis ranked highest in the dissimilarity index. Among metropolitan areas, Chicago, New York and Philadelphia did.

Since 1960, the share of blacks living in neighborhoods where they account for a minority of the population has risen to 59 percent from 30 percent.

"While it may be tempting to see the overwhelmingly white nature of many suburbs as evidence of stagnation or stasis, the presence of even modest numbers of African-Americans in suburbs demonstrates the remarkable change in American society," the study said. "Indeed, measured by dissimilarity indices, suburbs are often among the most integrated parts of America."

Only 424 of the nation’s 72,531 census tracts recorded no black residents. More than half were either in rural areas or in metropolitan regions where blacks account for less than 1 percent of the population. Every census tract in Connecticut, Maryland and New Hampshire recorded at least one black resident.

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