A Graduate School of Design study due for release late next month predicts that almost 6000 rental apartments in Cambridge will be converted to condominium units during the next decade barring legislative intervention by the city.

The study also shows (in sharp contrast to a city study done two years ago) that most of the people displaced by condominium conversions in the city will be low-and moderate-income or elderly.

Fifteen Design School students finished the report earlier this month. Their findings, presented to the city's Community Development Department, show:

With inflation and other variables figured in, the city can expect between 5000 and 7000 units, 44 per cent of all rent-controlled apartments in the city, converted to condominiums by 1990;

A projected 58.2 per cent of the tenants in those units will be displaced, most because they cannot afford the unit or feel they are too old to purchase a home;

Of those displaced, more than half will have incomes below $15,000 a year and most will be elderly;

Most of those moving into the condominiums will have incomes above $25,000 and 85 per cent will be single or be childless couples;

Most conversions will continue in the Harvard Square area.

The report "shows the need for tight city controls on the growth of condominiums in the city," City Councilor David Sullivan said last night.

A recently passed city law, under challenge in district court, has apparently "dampened" condominium conversion in the city by requiring developers to obtain permits, Brian Tracy, one of the authors of the study, said yesterday.

A city study two years ago on condominium conversion concluded that the displaced tend to come from the same socio-economic bracket as those who purchase the condominiums.

"The buildings being converted then tended to be the nicer buildings in each area," Betty DesRosiers, a staff member in the Community Development Department, said yesterday. As a result, more of the buildings converted now contain poorer tenants, explaining the discrepancy, she added.

The group looked at every building in Cambridge with seven or more rent-controlled units, Thomas Gougeon, the student who headed the project, said yesterday.

"We tried to construct a simple model of what makes it attractive for a developer to convert a building into condominiums," he added.

John Yinger, assistant professor of City and Regional Planning, who advised the group working on the study, said the final report would not present policy recommendations.