agency under section 15(b)(1) of the Natural Gas Act for the purposes of complying with the National Environmental Policy Act of 1969 ( 42 U.S.C. 4321 et seq. ) with respect to an authorization under section 3 of the Natural Gas Act or a certificate of public convenience and necessity under section 7 of such Act, the Commission shall, in accordance with this section and other applicable Federal law— (1) be the only lead agency