From the Greater Washington Research Center's recent report "The Changing Population of the District of Columbia" by Eunice S. Grier:

The District has had more people moving out than in at least since the 1950s, when the suburban home-buying boom moved into high gear. This type of movement results in what demographers call ''net out-migration.''

During the 1950s and the first part of the '60s, most of the out-movers were white. In the late '60s and '70s, they were joined by blacks as racial barriers were breached in many suburban communities. The black out-migration caused the city's population to decline at a faster pace than the white out-migration had done. As a result, the city lost 118,000 people, 16 percent of its residents, in the 1970s. By the early '80's more than half of all blacks in the metropolitan area resided in the suburbs.

Out-migration during the '80s was much slower than in the previous decade, but still fast enough to reduce the city's population still further. Between 1980 and 1988, 44,000 more people moved out of the District than into it. Births have helped mitigate the population loss, however.

Migration into and out of the District of Columbia in the '80s has been highly selective. While more people moved out than in overall, some age groups gained while others were losing.

The out-movers included virtually all age groups over 25. They also included preschool-age children. The heaviest losses were among adults in their thirties, presumably the parents of those children.

Despite continuing overall losses through out-migration, the District has long demonstrated an attraction for people in early adulthood. The recent past is no exception. Between 1980 and 1985, the District gained an estimated 24,300 net in-migrants between the ages of 15 and 24. Black migration, both in and out, generally mirrored the overall pattern.

Many of the young in-migrants, both black and white, come here to work. They choose city residence partly because of its closeness to places of work and recreation. At least until recent years, many have been drawn to the city by the availability of more reasonably priced rental housing than generally found in the suburbs. Others come to study in local colleges and universities or for military assignments. The early adult years are the peak time for residence in group quarters such as college dorms or military barracks. Some of these young people may remain in the Washington area when they complete their schooling or military assignment.

However, when these young people get married and start having children, many leave the city for the suburbs -- hence the net out-migration of persons beginning in the mid-twenties. In the 1950s and 1960s, almost all of the out-migrating young families were white. In the 1970s, most were black. In the first part of the 1980s, blacks have continued to predominate among the young out-movers, but there are many whites as well.

A new factor in the recent situation has been net-out migration of people in the older middle-aged brackets, especially 50 years and above. While their numbers are not as large as those of younger adults, they are substantial. People this age have not usually moved in such numbers in the past.

The recent out-migration may have been at least partly retirement-related. The federal government and many private-sector firms were encouraging older workers to retire early in this period, and considerable numbers may have chosen to move out of the Washington area to places where climates are warmer and living costs lower. If most have moved out of the area altogether and early retirement is the main factor, then the out-migration may be self-limiting. But the Research Center's "Census 86" survey found that many people who had recently moved to the suburbs from the District fit the profile of these older out-migrants.

This development needs careful watching. For decades, the District has experienced the recurring cycle of young people first moving in and then moving out again, often within a span of 10 years or less. Since they were constantly being replaced by other young people, there was little if any damage to the District's overall population structure or to its tax base.

But if middle-aged and older residents -- black as well as white -- have begun moving out of the District for the suburbs, in addition to retirement communities in the Sunbelt, this is a new and worrisome development. The District is losing some of its mature citizens, many in their peak earning years. Their residence is important to the city's continuing fiscal stability and civic vitality.