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NEW YORK, Dec 23 (Reuters) - Freddie Mac, the second-largest U.S. home funding provider, said its retained mortgage portfolio surged by a record annual rate of 65.6 percent in November, the second full month the company was under government control.

Freddie Mac's (FRE.P: Quote, Profile, Research) (FRE.N: Quote, Profile, Research) portfolio grew to $805.4 billion last month, up 12.8 percent year to date, the company said in its monthly volume summary.

It was the second straight month of significant growth in the company's mortgage investments, following two straight months of steep reductions. In October, the portfolio jumped by an annual rate of 43.6 percent.

Under the terms of its conservatorship, Freddie Mac, like its larger counterpart Fannie Mae (FNM.N: Quote, Profile, Research) (FNM.P: Quote, Profile, Research), can increase the portfolio to $850 billion by the end of next year. The government has relied on Fannie and Freddie to purchase mortgage assets to help fill absences of private mortgage banks and to stabilize housing markets.

The company's total mortgage portfolio rose at an annual rate of 2.8 percent in the month and by 5.1 percent in the first 11 months of the year.

Freddie Mac agreements to buy and sell mortgages for its portfolio declined in November to $15 billion from $17.4 billion the prior month.

The delinquency rate on single-family loans guaranteed by Freddie Mac kept rising in November, to 1.52 percent from 1.34 percent in October and well above 0.60 percent a year ago.

A Freddie Mac spokeswoman confirmed that the month's annual portfolio increase was a record but declined further comment.

(Reporting by Lynn Adler, Editing by Chizu Nomiyama)