In order (1) to facilitate the disposition of the surplus power of the Corporation according to the policies set forth in this chapter; (2) to give effect to the priority herein accorded to States, counties, municipalities, and nonprofit organizations in the purchase of such power by enabling them to acquire facilities for the distribution of such power; and (3) at the same time to preserve existing distribution facilities as going concerns and avoid duplication of such facilities, the Board is authorized to advise and cooperate with and assist, by extending credit for a period of not exceeding five years to, States, counties, municipalities and nonprofit organizations situated within transmission distance from any dam where such power is generated by the Corporation in acquiring, improving, and operating (a) existing distribution facilities and incidental works, including generating plants; and (b) interconnecting transmission lines; or in acquiring any interest in such facilities, incidental works, and lines.