The Secretary of the Treasury is authorized, upon request of the Secretary of the Interior and upon approval of the President, to transfer from time to time to the credit of the reclamation fund created by section 391 of this title, such sum or sums, not exceeding in the aggregate $5,000,000, as the Secretary of the Interior may deem necessary for the construction and operation of reclamation projects authorized under the Act of June 17, 1902 (32 Stat. 388), and under way on March 3, 1931, and Acts amendatory thereof or supplementary thereto.