The Secretary may, for purposes of all laws administered by the Department, accept uncompensated services, and enter into contracts or agreements with private or public agencies or persons (including contracts for services of translators without regard to any other law), for such necessary services (including personal services) as the Secretary may consider practicable. The Secretary may also enter into contracts or agreements with private concerns or public agencies for the hiring of passenger motor vehicles or aircraft for official travel whenever, in the Secretary’s judgment, such arrangements are in the interest of efficiency or economy.