An agency which, on September 15, 1961, was not authorized to transact any business or exercise any powers by a resolution adopted prior to such date, shall not transact any business or exercise any powers under this part unless, by ordinance, the legislative body declares that there is need for an agency to function in the community. The ordinance of the legislative body declaring that there is need for an agency to function in the community shall be subject to referendum as prescribed by law for a county or a city ordinance.