In meeting the housing needs of persons and families of low or moderate income, not less than 30 percent of the units financed by mortgage loans or property improvement loans pursuant to this part shall be available to, or occupied by, very low income households at affordable rents, unless it is not possible to obtain subsidies necessary to meet such requirement. No development loan, rehabilitation loan, or construction loan shall be made pursuant to this part if the agency determines that its ability to utilize currently available subsidies to meet the requirements of this section would be jeopardized thereby.