NEW YORK - Freddie Mac's (FRE.N) mortgage investment portfolio shrank in November while the rate of delinquencies on the loans in guarantees escalated, the U.S. home funding company said on Wednesday.

The unpaid principal balance of its mortgage-related investments fell at a 12.9 percent annual rate last month to $761.8 billion, for a 5.8 percent drop through the first 11 months of the year.

At the 2009 peak, the retained mortgage assets were about $867 billion in March.

The steady decline comes as mortgage securities got rich to purchase while the Fed has sopped up more than $1 trillion of the securities to help keep down mortgage rates and revive the housing market.

The company, as well as Fannie Mae (FNM.N) -- both taken under government control in September 2008 as loan failures ate away at capital -- is mandated to reduce the portfolio by 10 percent annually starting in 2010.

As the portfolio contracts, so does the company's outstanding debt. The total outstanding fell to $809.2 billion in November from $814 billion in October, having reached its high this year of $932 billion in March.

The delinquency rate on Freddie Mac's single-family mortgage portfolio, meantime, jumped 18 basis points to 3.72 percent in November. One year earlier the rate was 1.52 percent.

The multifamily loan delinquency rate rose to 0.14 percent from 0.12 percent in October and from just 0.01 percent a year earlier.

Freddie Mac said its refinance loan purchase and guarantee volume rose to $19.3 billion in November from $18 billion in October.

There were 7,313 borrowers as of November 30 that had made their last trial period payment and completed the required documentation for the Obama administration's Home Affordable Modification Program, the company reported. (Reporting by Lynn Adler, Editing by Chizu Nomiyama)