Each building or part of a building that is constructed or altered by, on behalf of, or for the use of the agency shall be designed, constructed, or altered so as to be readily accessible to and usable by handicapped persons. The definitions, requirements, and standards of the Architectural Barriers Act (42 U.S.C. 4151 through 4157), as established in 41 CFR 101-19.600 to 101-19.607, apply to buildings covered by this section.