Interest rates on long-term mortgage loans fell to another all-time low this week, breaking the 5 percent barrier, according to mortgage giant Freddie Mac Thursday.

“Interest rates for 30-year fixed rate mortgages fell for the 11th straight week to another record low, due in part to the slowing economy and government actions,” said Frank Nothaft, Freddie Mac vice president and chief economist.

“So far,” he explained, “both the U.S. Treasury Department and the Federal Reserve have added over $100 billion in liquidity to the mortgage market since September 2008, which put downward pressure on interest rates for fixed-rate mortgages. The Federal Reserve may add up to an additional $570 billion more this year, based on its November 25, 2008 announcement, to further shore up mortgage lending and keep rates low.”

The average rate on a 30-year fixed rate mortgage dropped to 4.96 percent, excluding fees, during the week ended January 15, 2009, down from 5.01 percent the previous week. The rate has never been below 5 percent since Freddie Mac began keeping track of weekly rates in 1971. One year ago, the average rate was 5.69 percent.

Rates on 15-year fixed rate loans increased slightly however in the latest week with the average growing to 4.65 percent from 4.62 percent one week earlier. Last year at this time, the average rate was 5.21 percent.

One-year adjustable rate mortgages carried an average rate of 4.89 percent, down from 4.95 percent the week before. During the same week of January 2007, one-year ARM rates were higher than even fifteen-year FRM rates at 5.26 percent.

Meanwhile, during roughly the same week, the Federal Reserve bought up $23.4 billion of mortgage-backed bonds from Fannie Mae, Freddie Mac, and Ginnie Mae in an attempt to keep rates low and pump liquidity back into the lending markets.