A federal judge has rejected a tenants group's allegations that managers of The Point, a high-rise apartment complex in Silver Spring, last year attempted to drive black families from one of the development's three buildings.

"The Court finds that the decision to convert Building Three to an all-adult building was based on purely economic factors and that racial considerations were not a factor in that decision," Judge Norman Ramsey of the U.S. District Court in Baltimore wrote in an opinion released last week.

Forty-one tenants, most of them black, sued the development's managers last year charging that the proposed exclusion of children would disproportionately affect the building's black residents, who more commonly had children, and was really intended to alter racial composition.

The defendants -- the Boston-based management firm Krupp Associates, three of its top executives and an affiliated company -- argued successfully that the conversion was intended to avoid costs of repairing children's vandalism and to meet a high demand for all-adult living environments in Montgomery County.

The plaintiffs failed to show an intent to discriminate against minorities, the judge concluded. Moreover, he wrote, although the conversion initially would fall more heavily on blacks than whites, there was no evidence that it would have that effect on a continuing basis.

Dominating the intersection of Columbia Pike and New Hampshire Avenue, The Point's three towers contain 1,119 units, a major portion of the county's supply of rental housing. The complex was taken over in 1979 by Krupp Associates, which began an extensive program of renovation.

Last summer, Krupp announced that Building Three would be converted to all-adult status. Tenants with children received notices to leave when their leases expired, with an offer of comparable apartments in The Point's other two buildings.

Citing incidents of alleged racial harrassment of black tenants by white staff members, the tenants group filed suit last summer under the Civil Rights Act of 1968 and other laws in an attempt to block the conversion. It was suspended pending the trial, which heard testimony from 27 witnesses.

In his opinion, Judge Ramsey labeled as not credible two key witnesses against Krupp, both of them former employes of the company who testified they wre instructed to discriminate against black tenants.

Helen Guerra, a former resident manager, testified that a Krupp vice president, believing that prospective tenants were put off by seeing large numbers of black children in the swimming pool, ordered her to "get them out."

Guerra's employment at The Point ended in August 1980.

Judge Ramsey noted conflicting testimony from defense witnesses and said that Guerra clearly harbored deep resentment toward the firm due to her termination. "Her demeanor on the stand, her tone of voice and the style of responses all reeked of animus and vindictiveness," the opinion said.

Kerry Scanlon, an attorney for the plaintiffs, said his side would seek to have Judge Ramsey amend his decision on the grounds that it contains legal errors, failed to consider certain evidence and is unclear on some issues.