In general .—

The Secretary is authorized to enter into annual contributions contracts with public housing agencies pursuant to which such agencies may enter into contracts to make assistance payments to owners of existing dwelling units in accordance with this section. In areas where no public housing agency has been organized or where the Secretary determines that a public housing agency is unable to implement the provisions of this section, the Secretary is authorized to enter into such contracts and to perform the other functions assigned to a public housing agency by this section.