“That the Secretary is authorized to issue commitments for direct loans to public agencies in accordance with section 627 of the Public Health Service Act [42 U.S.C. 291j–7] which shall constitute contractual obligations of the United States, the total of such outstanding commitments not to exceed $30,000,000 at any given time; to sell obligations received pursuant to such commitments as provided in section 627, and the proceeds of any such sale shall be used to make a direct loan pursuant to the outstanding commitment under which the obligations were received.”