Before awarding any contract for such work to be done in a project, the agency shall ascertain the general prevailing rate of per diem wages in the locality in which the work is to be performed, for each craft or type of workman needed to execute the contract or work, and shall specify in the call for bids for the contract and in the contract such rate and the general prevailing rate for regular holiday and overtime work in the locality, for each craft or type of workman needed to execute the contract.