For the third straight week, long-term U.S. mortgage interest rates continued to climb, spurred by higher bond yields and reports of a slowing economy, according to mortgage company Freddie Mac Thursday.

The average rate on a 30-year fixed rate home loan grew to 5.15 percent, excluding fees, during the week ended March 5, 2009, up from 5.07 percent the previous week. The current rate is still very low by historical standards though. One year ago, the average rate was almost an entire percentage point higher at 6.03 percent.

“Mortgage rates followed bond yields higher this week following reports of record continuing jobless claims and a downward revision in economic growth in the fourth quarter of 2008,” said Frank Nothaft, Freddie Mac vice president and chief economist. “Real Gross Domestic Product was revised from a 3.8 percent decline to a 6.2 percent drop in the fourth quarter mostly led by a 4.3 percent fall in consumer spending, which was the largest decrease since the second quarter of 1980.”

“The housing market continues to slow as well,” Nothaft added. “New home sales fell 10.2 percent in January to the slowest pace since records began in January 1963 while pending existing home sales slowed by 7.7 percent, the weakest since the series began in January 2001. More recently the Federal Reserve noted in its March 4th regional economic report that residential real estate markets remained in the doldrums in most areas, with only scattered, very tentative signs of stabilization.”

Rates on other common mortgage loans also rose in the latest week, with the average interest rate on a 15-year fixed rate loan increasing to 4.72 percent, up from 4.68 percent one week earlier. Last year at this time, the average rate was 5.47 percent.

On-year adjustable rate mortgages (ARMs) rose to 4.86 percent from 4.81 percent. During the same week of March 2008, the average rate was 4.94 percent.