Any function described in section
7172 of this title which relates to the establishment of rates and charges under the Federal Power Act [
16 U.S.C.
791a et seq.] or the Natural Gas Act [
15 U.S.C.
717 et seq.], may be conducted by rulemaking procedures. Except as provided in subsection (d) of this section, the procedures in such a rulemaking proceeding shall assure full consideration of the issues and an opportunity for interested persons to present their views.