((a)) Notwithstanding any other provision of this chapter, the purchase by the Bank of the obligations of any local public body or agency within the United States shall be made upon such terms and conditions as may be necessary to avoid an increase in borrowing costs to such local public body or agency as a result of the purchase by the Bank of its obligations. The head of the Federal agency guaranteeing such obligations, in consultation with the Secretary of the Treasury, shall estimate the borrowing costs that would be incurred by the local public body or agency if its obligations were not sold to the Bank.

((b)) The Federal agency guaranteeing obligations purchased by the Bank may contract to make periodic payments to the Bank which shall be sufficient to offset the costs to the Bank of purchasing obligations of local public bodies or agencies upon terms and conditions as prescribed in this section rather than as prescribed by . Such contracts may be made in advance of appropriations therefor, and appropriations for making payments under such contracts are hereby authorized.