(a) Aggregate fiscal year limitation
Notwithstanding any other provision of law and subject only to the absence of qualified applicants or proposed activities and to the authority provided in this subchapter, to the extent approved or provided in appropriations Acts, the Secretary may enter into commitments to guarantee notes and obligations under this subchapter with an aggregate principal amount not to exceed $400,000,000 for each of fiscal years 2009 through 2013.

(b) Authorization of appropriations for credit subsidy
There are authorized to be appropriated to cover the costs (as such term is defined in section 661a of title 2) of guarantees under this subchapter such sums as may be necessary for each of fiscal years 2009 through 2013.

(c) Aggregate outstanding limitation
The total amount of outstanding obligations guaranteed on a cumulative basis by the Secretary pursuant to this subchapter shall not at any time exceed $2,000,000,000 or such higher amount as may be authorized to be appropriated for this subchapter for any fiscal year.

(d) Fiscal year limitations on tribes
The Secretary shall monitor the use of guarantees under this subchapter by Indian tribes. If the Secretary finds that 50 percent of the aggregate guarantee authority under subsection (c) has been committed, the Secretary may—

(1) impose limitations on the amount of guarantees any one Indian tribe may receive in any fiscal year of $50,000,000; or

(2) request the enactment of legislation increasing the aggregate outstanding limitation on guarantees under this subchapter.