In addition to the number of positions which may be placed at GS–16, GS–17, and GS–18 under section
5108 of title
5, under existing law, or under this chapter, and to the extent the Secretary deems such action necessary to the discharge of his functions, he may appoint not more than two hundred of the scientific, engineering, professional, and administrative personnel 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.