The provisions of Federal reclamation laws (Act of June 17, 1902, 32 Stat. 388, and Acts amendatory thereof and supplemental thereto) which limit the acreage of irrigable land which may receive irrigation benefits from, through, or by means of Federal reclamation works, shall not be applicable to lands owned by States, political subdivisions, and agencies thereof, so long as such lands are farmed, primarily in the direct furtherance of a non-revenue-producing public function, as determined by the Secretary of the Interior; and to the extent that such lands continue to qualify for the exempted status afforded by this section they shall not be deemed to be excess lands for any purposes whatsoever under said reclamation laws.