Bonds of any local public housing agency (as defined in the United States Housing Act of 1937, as amended) as are secured either, (

a) by an agreement between the public housing agency and the Public Housing Administration in which the public housing agency agrees to borrow from the Public Housing Administration, and the Public Housing Administration agrees to lend to the public housing agency, prior to the maturity of those obligations (which obligations shall have a maturity of not more than months), moneys in an amount which (together with any other moneys irrevocably committed to the payment of interest on the obligations) will suffice to pay the principal of those obligations with interest to maturity thereon, which moneys under the terms of that agreement are required to be used for the purpose of paying the principal of, and the interest on, those obligations at their maturity, or (

b) by a pledge of annual contributions under an annual contributions contract between the public housing agency and the Public Housing Administration if the contract shall contain the covenant by the Public Housing Administration which is authorized by subsection (

b) of

Section of the United States Housing Act of 1937, as amended, and if the maximum sum and the maximum period specified in the contract pursuant to subsection (

b) of

Section of the United States Housing Act of shall not be less than the annual amount and the period for payment which are requisite to provide for the payment when due of all installments of principal and interest on those obligations.