such percentage of that sum (but at least 30 percent and not more than 60 percent) as is considered appropriate by the Secretary, which can be matched with non-Federal moneys in accordance with the requirements of subsection (b) of this section, less such amount (but not more than 4 percent of such percentage) considered necessary by the Secretary to defray the costs of administering this chapter during such fiscal year, shall be allocated by the Secretary to carry out approved wetlands conservation projects in Canada and Mexico in accordance with section 4405(b) of this title; and

the remainder of such sum after paragraph (1) is applied (but at least 40 percent and not more than 70 percent), which can be matched with non-Federal moneys in accordance with the requirements of subsection (b) of this section, shall be allocated by the Secretary to carry out approved wetlands conservation projects in the United States in accordance with section 4405(a) of this title.

Except as provided in paragraph (2), as a condition of providing assistance under this chapter for any approved wetlands conservation project, the Secretary shall require that the portion of the costs of the project paid with amounts provided by non-Federal United States sources is equal to at least the amount allocated under subsection (a) that is used for the project.

Federal moneys allocated under subsection (a) may be used to pay 100 percent of the costs of such projects located on Federal lands and waters, including the acquisition of inholdings within such lands and waters.

The non-Federal share of the United States contribution to the costs of such projects may not be derived from Federal grant programs. In the case of a project carried out in Canada or Mexico, the non-Federal share of the costs of the project may include cash contributions from non-United States sources that are used to pay costs of the project. In the case of a project carried out in Canada, funds from Canadian sources may comprise up to 50 percent of the non-Federal share of the costs of the project.

The Secretary may from time to time make payments to carry out approved wetlands conservation projects as such projects progress, but such payments, including previous payments, if any, shall not be more than the Federal pro rata share of any such project in conformity with subsection (b) of this section.

The Secretary may enter into agreements to make payments on an initial portion of an approved wetlands conservation project and to agree to make payments on the remaining Federal share of the costs of such project from subsequent allocations if and when they become available. The liability of the United States under such an agreement is contingent upon the continued availability of funds for the purposes of this chapter.