Freddie Mac announced today that its mortgage investment portfolio grew by an annualized 7.3 percent rate in September, while delinquencies on loans it guarantees accelerated.  The portfolio increased to $784.2 billion, for an annualized 3.4 percent decrease year to date, and delinquencies, which increase stress on the company's capital, jumped to 3.33 percent of its book of business in September from 3.13 percent in August and 1.22 percent in September 2008. The multifamily delinquency rate accelerated slightly in September to 0.11 percent from 0.10 percent in August. A year earlier it was 0.01 percent.