(a) A claim of the United States against a person arising out of an erroneous payment of pay or allowances made on or after July 1, 1960, or arising out of an erroneous payment of travel, transportation or relocation expenses and allowances, to an employee of an agency, the collection of which would be against equity and good conscience and not in the best interests of the United States, may be waived in whole or in part by- (1) the authorized official; (2) the head of the agency when- (A) the claim