The low-down-payment loans are the centerpiece of many lenders' affordable- housing programs. Mr. Brendsel said Freddie Mac believes delinquencies are higher because such borrowers are not required to hold the customary one-month reserve of principal and interest payments that other borrowers must show. In addition, he said, such borrowers may have poor credit histories. As a result Mr. Brendsel said, Freddie Mac plans to stop some of its experimentation. For example, the agency will no longer buy loans with a 5% down payment where 2% is given by a third party. In addition, Freddie Mac has instructed lenders to intensively underwrite low-down-payment loans to borrowers with weak credit histories. The agency itself will scrutinize these loans more closely, according to its chairman.