Whenever real property is acquired by the government of the District of Columbia or the Washington Metropolitan Area Transit Authority for a program or project which is not subject to sections 4630 and 4631 of this title, and such acquisition will result in the displacement of any person on or after January 2, 1971, the Mayor of the District of Columbia or the Washington Metropolitan Area Transit Authority, as the case may be, shall make all relocation payments and provide all assistance required of a Federal agency by this chapter. Whenever real property is acquired for such a program or project on or after such effective date, such Mayor or Authority, as the case may be, shall make all payments and meet all requirements prescribed for a Federal agency by subchapter III of this chapter.