Freddie Mac (FRE) committed to buy $25.365 billion of mortgage bonds in December.

The mortgage giant's total investment portfolio balance was at $804.8 billion as of the end of 2008, more than $45 billion shy of the $850 billion limit set by its regulator when the mortgage finance giant was nationalized last September, according to a monthly summary from the company. Freddie's portfolio was at $720.81 billion as of December 2007.

Over the past couple of months, the role of Freddie and its sibling Fannie Mae (FNM) in the mortgage market have diminished as both the U.S. Treasury and the Federal Reserve have emerged as backstop buyers with deep pockets.

The U.S. Treasury, so far, has bought nearly $75 billion of agency mortgage-backed securities, while the central bank bought $52.63 billion.

However, market participants still keep tabs on Fannie and Freddie's portfolios as an indication of their financial health and their ability to continue to play a role as both guarantors and buyers of mortgage bonds.

Freddie's report also gave an indication of the extent of decline among prime borrowers with conforming loans, as its single-family delinquency rate continued to rise sharply. In December, the rate rose to 1.72% from 1.52% in November, and 0.65% at the end of 2007.

Meanwhile, Freddie's issuance of guaranteed securities and pass-through certificates increased to $15.72 billion from $14.5 billion in November.

The mortgage giant's total mortgage portfolio grew 4.1% in December and 5% for the year, to $2.21 trillion.

The duration gap, a measure of the portfolio's sensitivity to interest rates, averaged one month in December.

-By Prabha Natarajan, Dow Jones Newswires, 201-938-5071; prabha.natarajan@dowjones.com

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