It is declared to be the policy of this subchapter to further the national defense by providing housing in those areas where it cannot otherwise be provided by private enterprise when needed, and that such housing may be sold and disposed of as expeditiously as possible: Provided, That in disposing of said housing consideration shall be given to its full market value and said housing or any part thereof shall not, unless specifically authorized by Congress, be conveyed to any public or private agency organized for slum clearance or to provide subsidized housing for persons of low income: Provided further