Subject to the provisions of this subchapter, the Secretary of Defense (hereafter in this subchapter referred to as the "Secretary") shall prescribe such regulations relating to continuing security procedures as he considers necessary to assure - (1) that no person shall be employed in, or detailed or assigned to, the National Security Agency (hereafter in this subchapter referred to as the "Agency"), or continue to be so employed, detailed, or assigned; and (2) that no person so employed, detailed, or assigned shall have access to any classified information; unless such employment, detail, assignment, or access to classified information is clearly consistent with the national security.