The Alexandria City Counil pledged its renewed support yesterday to a developer's proposal for refurbishing the city's Shirley-Duke apartment complex in hopes the federal government will guarantee $53 million in loans for the work.

A key feature in the developer's proposal has been a promise to convert 423 of the 2,100 units in the project into rental units for low- and moderate-income families. Earlier this week developer Morton Sarubin threatened to turn the entire project into condominiums and apartments for the wealthy if the city refused to issue him a building permit by Sept. 30.

But yesterday City Councilman Donald C. Casey said the city had devised a proposal that he said would "save the project." City officials had said previously that they would be unable to issue the permit by the end of the month because of various technical reasons.

Sarubin had told the council he feared the Department of Housing and Urban Development would drop its promise of loan guarantees for the project unless he had the permit by then, William Tennant, a lawyer representing Sarubin, said yesterday he was "95 percent sure" the resolution of support would be an adequate replacement for the permit.

The Shirley-Duke project in the south portion of the city near Cameron Station, was built after World War II as housing for returning veterans. Before its closing two years ago, it was a major source of low income housing in Northern Virginia.

City officials have been fearful that if the project is reopened entirely as low income housing it might again become a source of overcrowding and crime.