The Bush administration is preparing a request for $40 million to $50 million in humanitarian aid to sustain the Nicaraguan Contra rebels until the promised date for elections in Nicaragua, officials said Tuesday. After extensive review and consultation with Congress, the officials said the administration may this week announce a policy shaped by diplomatic developments in Central America and political realities on Capitol Hill. President Bush, who has promised to not abandon the Contras, is expected to ask Congress for enough non-military aid to keep them intact until Feb. 25, 1990, the date Nicaraguan President Daniel Ortega has set for elections.