An influx of blacks, Asians and Hispanics dramatically changed the composition of the Maryland suburbs during the last decade, the Census Bureau reported yesterday.

The greatest transition occurred in Prince George's County, where blacks fanned out from neighborhoods along the District border into almost all areas of the county and increased from 13.9 percent of the county's population in 1970 to 37.3 today. At that same time the county's total population increased only minmally from 661,719 to 665,071 as the county's white population dropped by almost one third.

Montgomery County, for years an overwhelmingly white suburb, lost some of its homogeneity as the percentage of black residents grew from 4.1 percent in 1970 to 8.8 percent of the county's 579,053 residents in 1980. During the same period Asians and other minorities increased from less than 1.5 percent in 1970 to nearly 6 percent today.

The Maryland figures are similar to those for Northern Virginia released earlier in the week which also document a sharp increase in the number of blacks, Asians, and Hispanics. The changes in Virginia and Maryland suburbs occurred, according to census figures, at the same time as the black population in Washington declined for the first time in more than 10 years. The District's overall racial composition remained the same, however, because of simultaneous decreases in the number of white residents.

Statewide, the number of blacks and other minorities in Maryland increased from 18.5 percent of the state's 3.9 million residents in 1970 to a quarter of the state's 4.2 million in 1980.In Baltimore, which lost some 120,000 residents during the 1970s, blacks grew from 46 percent of the city's 1970 population to over half the city's 786,775 population in 1980.

"These figures say there has been a tremendous movement of blacks to the suburbs, which shows that desegregation is going on here," said George Grier, a demographer who has extensively studied the Washington area. "There has also been a continuing spread of blacks in the suburbs so that they are no longer living just in certain areas along the District's borders," he said.

Although all Washington suburbs showed an increase in black population during the 1970s, the greatest growth occurred in Prince George's County, where the racial composition returned to what it was during the county's tobacco farming, sharecropper days at the turn of the century.

The increase, from 91,808 blacks residents in 1970 to 247,860 of 665,071 total population in 1980, came at a time of profound social turmoil in the county as its residents faced rapid urbanization and a variety of racial issues including court-ordered busing for desegreation and blacks demands for greater political power.

The impact of the increase in black residents goes beyond simple numbers. In 1970, two-thirds of the county's blacks were clustered in a few mostly poor communities just across the District border, where the only affordable housing available to them was located.

In 10 years time, the county has seen black families, many of whom are middle- upper middle-income professionals, moving into almost all areas of the county and integrating many overwhelming white sections such as Oxon Hill and Tantallon in the south Hyattsville and Bladensburg in the north.

In most cases, these new, more affluent families moved in and replaced white families, Grier said, who moved to more expensive housing elsewhere. During the decade the county's white population dropped 170,049.

"The figures are not particularly surprising," said Prince George's County Council chairman Parris Glendening. "It's part of a historial pattern -- blacks, like other individuals, are leaving the central city.They want a single-family home in the suburbs and Prince George's has been able to provide it at an affordable cost. We have seen a gradual process of change."

In Montgomery, the black population increased from 21,551 out of 522,809 county residents in 1970 to 50,756 out of 579,053 in 1980, with the Wheaton area experiencing a three-fold growth in black residents. Blacks now constitute 8.8 percent of Montgomery's population, the highest percentage recorded since the 1940 census.

A more dramatic proportional increase over the last 10 years occurred in the number of Asians living in Montgomery. In 1970, the census registered 7,324 other minorities, primarily Asians; by 1980 that figure had more than quadrupled to 32,812, with much of that increase in Rockville and Wheaton.

"We've had a tremendous migration of Asians into the United States and particularly this area," said Grier. "It's the fastest growing minority group in this area from all the evidence we have. A lot of them were landed gentry and were therefore able to afford the cost of housing in Montgomery."

Montgomery officials said they were not surprised by the new census figures, although a spokesman for County Executive Charles Gilchrist said that Gilchrist had expected that the black population in the county would be somewhat larger than reported by the Census Bureau. "It's not that big in percentages but it gives the county a bit more of a cosmopolitan nature," said spokesman Charles Maier. "I think we can assimilate miniorities. I think it adds vitality," he said.