Melvin Watt, Federal Housing Finance Agency chief, has announced a program offering more reassurances to mortgage banks that fear they could suffer unpredictable losses on the loans they sell to the government. The housing finance agency intends to relax the agreements that determine when Fannie and Freddie may require banks to buy back bad loans. Under the new program, the agencies would only demand buybacks when there is a pattern of misrepresentations and inaccuracies in the loans. The move is intended to reassure banks that have had to pay tens of billions of dollars to settle legal cases arising from the housing boom and bust and buy back bad loans sold to Fannie and Freddie.