Subject to the limitations provided in paragraph (2) and to the extent the Secretary deems such action necessary to the discharge of his functions, he may appoint not more than three hundred eleven of the scientific, engineering, professional, and administrative personnel of the department without regard to the civil service laws, and may fix the compensation of such personnel not in excess of the maximum rate payable for GS–18 of the General Schedule under
section 5332 of title 5.