the term “eligible metropolitan area” means any Metropolitan Area (as such term is defined by the Office of Management and Budget pursuant to
section 3504 of title 44) with a 1980 population of 250,000 or more that has been designated by a proposer and the Secretary for a demonstration project under this subchapter, except that the Secretary may designate an area with a 1990 population of 50,000 or more as an eligible metropolitan area;