Freddie Mac (FRE) mortgage delinquencies continued to rise in January, even though the volume of the GSE's total mortgage portfolio is declining. Furthermore, a credit rating agency hints at deeper woes for the firm as mortgage-backed securities (MBS) investors who bought in at premium rates are now at risk of seeing a drop in their net investment. The delinquency rate on Freddie's single-family loans grew to 4.03% in January, up from 3.87% in December, according to a monthly volume summary (available to download here). A year ago, the delinquency rate was 1.98%. At the same time, the total mortgage portfolio decreased at an annualized rate of 1.7% in January. The new figures arrive as Brian Harris, a senior vice president of the financial institutions group at Moody's Investors Service, warns of other difficulties within agency MBS, like those issued by Freddie. Harris said in monthly commentary provided to HousingWire, that agency MBS investors will likely see their net investment decline because of the recently announced delinquent loan buyouts at both Freddie and Fannie Mae (FNM) Freddie Mac is expected to complete the majority of its repurchases this month, providing capital preservation, however, Fannie's will take some more time, Harris said. As HousingWire's Linda Lowell previously reported, both government-sponsored enterprises (GSEs) announced moves to buyout delinquent loans — repurchases Harris noted "will preserve the GSEs' capital" in the wake of Financial Accounting Standards (FAS) 166 and 167 implementation. Freddie's refinance-loan purchase and guarantee volume was $22.6bn in January, down from $27.3bn in December. Total guaranteed purchase coupons (PCs) and structured securities issued decreased at an annualized rate of 0.5% in January. Freddie reported $36.6bn of purchases and issuances for January. This month's issuance includes $7.2bn of guarantees under the Housing Finance Agencies initiative, Freddie said. Freddie also announced Friday a move to stop purchasing and securitizing interest-only mortgages on Sept. 1, 2010. Write to Diana Golobay. Disclosure: The author holds no relevant investment positions.