Displacement of inner-city poor families by middle-class home buyers, a phenomenon that has become widespread in Washington, is growing rapidly in other major cities as well, witnesses testified yesterday before the Senate Committee on Banking Housing and Urban Affairs.

Witnesses from New York City, the District of Columbia, Baltimore and Harford, Conn., told the committee - in the first of two days of hearings, which will conclude today - that many poor and frequently minority residents of the nation's inner city areas are being forced from their central city neighborhoods.

Most of the witnesses agreed that neither the federal nor local governments have so far had much success in efforts to come to grips with the problem of dislocation.

The phenomenon in many respects resembles a round of "musical chairs" in which middle-class residents who fled the inner city a decade ago were replaced by the poor. Now it appears that many of the poor residents will be shuttled to the suburbs as the upper classes once again occupy the cities, witnesses maintained.

"As suburaban housing costs rise and as it becomes more and more expensive to commute long distanced to work, we are seeing an increased demand among middle and upper middle class people for housing in our cities," said Harford City Councilman Nicholas R. Carbone.

Carbone, who said 61 per cent of all Hartford residents live in incomes below the poverty level, said the city hopes to retain many of its low-income residents by creating, among other things, racially and economically diversified neighborhoods.

Robert C. Embry, assistant Secretary for Community Development of Housing and Urban Development, agreed that cities should strive to create economically and racially "intergrated" neighborhoods.

"If this long-sought goal of middle class interest in central city housing becomes a widespread reality," he said, "we must insure that the massive federal expenditures of the past which set the stage for this return to the city serve all the people."

Embry, who presented his testimony to Sen. William Proxmire (D-Wis.), chairman of the committee and the only member in attendance yesterday, said the stereotype of persons buying inner-city homes is that of affluent white suburbanites.

"That stereotype is not accurate," Embry said. "About 70 per cent of the home buyers are current city residents and a large number of them are blacks who are investing in homes in their own neighborhoods."

Embry added that many of the other central city home buyers are white young people wwo are not yet affluent, but who have great earning potential.

Frank Smith Jr. chairman of the Adams Morgan Organization here, told the committee about 26 low-income families on Seaton Street NW in the rapidly changing Adams Morgan community who received eviction notices in March 1976.

Although most of the families received cash payments or court orders to move, Smith said that nine of the families refused to move and went to court to fight for their right to purchase their homes. Next week, Smith said, these nine families will go to settlement on their houses.

The Seaton Street families have been a rare exception to the rules which generally govern home buying in the Adams Morgan neighborhood, Smith said.

In a study he conducted, Smith said he found "two classes" of real estate sales occuring in Adams Morgan. One class of sales occurs when speculators sell houses to each other: the other occurs when speculators sell houses to individual purchasers - but usually not to the family renting the house at the time of the sale.