The Alexandria City Council last night approved a controversial zoning change that proponents said will enable the city's public housing authority to remain solvent at a time when shrinking federal housing subsidies are forcing some urban housing agencies into bankruptcy.

The council voted 6 to 1 to change the zoning from residential to commercial on a 6 1/2-acre tract next to the future Braddock Road Metro station. The site is now occupied by the 40-year-old, 90-unit John Roberts housing project.

The Alexandria Redevelopment and Housing Authority intends to sell the property, valued at $6 million to $10 million, to private developers and invest the money in a fund to maintain and expand public housing facilities in the city.

The housing authority plans to rehabilitate another public housing project in the Old Town area and build a new public housing high rise for the elderly to accommodate the John Roberts residents. A city law prohibits demolition of any public housing units until replacement housing is provided.

The rezoning and the ultimate sale of the John Roberts site, which is at least a year away, has drawn sharp criticism from various civic groups and citizen activists.

Some critics favor removing public housing from Alexandria. Civic associations of neighborhoods bordering the John Roberts site question the wisdom of changing the zoning before a specific development plan is in hand. Other civic activists oppose rezoning and eventual demolition of the project, saying it will destroy the John Roberts neighborhood, which they maintain could be easily rehabilitated.

But last night the majority of the council agreed with Housing Authority Director Angus T. Olson, who has argued that the John Roberts site will be too close to a busy Metro rail station to make it suitable for continued residential use.

Olson told the council that to delay a decision on the rezoning would be a damaging sign to potential developers who would be reluctant to draw up plans for the site as long as the project appeared to lack solid council backing.

The sole dissenting vote was cast by council member Nelson Greene, who said, "I have the same apprehension about this as some of the tenants. They want to see what's in store for the area before they move. They want to see what's coming."

But the rest of the council agreed with Mayor Charles Beatley, who said, "The issue is not whether we want to move in this direction, but whether we want to do it now or later."