Obligations of a local public agency (as defined in Section 110(h) of the federal Housing Act of 1949) or of a public housing agency (as defined in the federal Housing Act of 1937, as amended) which have a maturity of not more than 18 months if such obligations are secured by an agreement between the obligor agency and the Secretary of Housing and Urban Development in which the agency agrees to borrow from the Secretary, and the Secretary agrees to lend to the agency, prior to the maturity of such obligations, money in an amount which (together with any other money irrevocably committed to the payment of interest on such obligations) will suffice to pay the principal of such obligations with interest to maturity, which money under the terms of the agreement is required to be used for that purpose.