The longtime aide tapped by Vladimir V. Putin to be his successor as president of Russia declared Tuesday that he wanted Putin to be his prime minister, offering the clearest indication yet of how Putin plans to maintain firm control over the Kremlin after his term ends next spring. The announcement, in a speech to the nation by the aide, Dmitri A. Medvedev, raised the prospect of a stark realignment in the structure of the Russian government, which is currently led by a strong president who appoints a prime minister to serve largely as an administrator. Full Story