The Secretary may issue and have outstanding at any one time notes and other obligations for purchase by the Secretary of the Treasury in an amount which will not, unless authorized by the President, exceed $1,500,000,000. For the purpose of determining obligations incurred to make loans pursuant to this chapter against any limitation otherwise applicable with respect to such loans, the Secretary shall estimate the maximum amount to be loaned at any one time pursuant to loan agreements then outstanding with public housing agencies. Such notes or other obligations shall be in such forms and denominations and shall be subject to such terms and conditions as may be prescribed by the Secretary with the approval of the Secretary of the Treasury. The notes or other obligations issued under this subsection shall have such maturities and bear such rate or rates of interest as shall be determined by the Secretary of the Treasury. The Secretary of the Treasury is authorized and directed to purchase any notes or other obligations of the Secretary issued hereunder and for such purpose is authorized to use as a public debt transaction the proceeds from the sale of any securities issued under chapter
31 of title
31, and the purposes for which securities may be issued under such chapter are extended to include any purchases of such obligations. The Secretary of the Treasury may at any time sell any of the notes or other obligations acquired by him under this section. All redemptions, purchases, and sales by the Secretary of the Treasury of such notes or other obligations shall be treated as public debt transactions of the United States.