Many of yesterday's bedroom communities are rapidly becoming today's small and middle-sized cities, ranging in population from 10,000 to 500,000 persons, according to a new urban study by the Joint Center for Political Studies.

The population growth of the new cities is being fueled by a continuing exodus from larger urban areas, the report said. This increasing diversity in communications and other business technology has made it easier for companies to move into the newer, often more lucrative job markets, and, by the annexation of formerly unincorporated suburban areas, to existing towns, it noted.

"The evidence is clear. An increasing number of United States central cities, and a widening ring of their older suburbs, must now learn to live and cope with population decline," wrote Brian J. L. Berry, a Harvard urbanologist. Berry is one of 34 contributors to the 380-page study, entitled "Small Cities in Transition: The Dynamics of Growth and Decline."

"Half-way through the decade, the central cities of U. S. metropolitan areas already have lost 3.1 percent of their 1970 residential population," Berry said. He said suburban areas grew by 9.3 percent in the same period, and that the suburbs "are the home of 38.9 percent of the nation's population, as compared to 29.2 percent for central cities and 32 percent for nonmentropolitan areas, which are growing once again."

The study said the Washington metropolitan area was typical of the shift to samll, self-contained cities that occured between 1960 and 1970.

"During that decade, the white population declined in the central city and grew in the Maryland and Virginia suburbs," the study said, "The black population of the metropolitan area increased both inside and outside of the central city," it said.

Between 1965 and 1970, some 568,000 persons moved into the Washington area, the study said. But it said only 14 percent of those people moved into the District. Of the new District residents, 49,000 were white and 32,000 were black. Members of both races came mainly from Maryland, Virginia and New York, the study said.

The study said.

The study citied Reston and Columbia as being typical of the burgeoning new communities. It also citied the Washington area as being one of 10 places experiencing a major movement of blacks to the suburbs.

Approximately 71.175 black persons moved to the Washington suburbs between 1960 and 1970, compared with 516,654 whites, according to the study.

However, Herrington J. Bryce, who directed the study, cautioned that the shift to smaller cities and self-contained suburban living is an "uneven" phenomenon.

Bryce said the South, for example, contains some of the nation's fastest-growing small cities, while it also contains some of those "which declined the fastest and some that are the poorest" in the country.

"Indeed, there are sharp differences between those small cities which are declining and those which are growing," said Bryce, who now serves as vice president of the Academy for Contemporary Problems, a state-municipal research group based in Columbus, Ohio.

"The fastest-growing small cities, as a rule, are lily white. Almost 68 percent of them had no nonwhites," he said in the study. On the other hand, many of the declining small cities had large black and other minority populations, Bryce said.

He said the growing cities may have obtained their predominantly white populations by "imposing exclusionary (tax and zoning) barriers against the black and the poor." Also, he said, many of the developing small cities " do not have the type of employment that would attract the unskilled in great numbers," because those cities "are not manufacturing centers."

Bryce said "we might be witnesses a rather interesting turn of events" in the shift to small and middle-sized cities.

"During the past decades the declining countries of the South were principally black," he said. "These countries declined as a result of the black exodus to the North. Today, declining cities have larger black populations than growing cities. This fact might be relate to immobility . . . Now, it might very well be that (blacks) may be tied to these (larger) manufacturing cities which are on the decline as new (smaller) nonmanufacturing cities which are on the decline as new (smaller) nonmanufacturing cities emerge."

He said the most rapidly growing small cities are concentrated in the West, with 16 of the top 50 in California, he said. The greatest concentration of rapidlydeclining small cities in the Northeast, which has no cities listed among the top 50 in terms of growth, Bryce said.

"Clearly, there is a high concentration among growth and region, even among small cities," he said.

Wilbur R. Thompson, an economics professor at Wayne State University, argued in the study that larger, older cities will continue to have advantages despite the increasing movementto small and middle-sized cities.