Mortgage interest rates fell for the third straight week but home sales remain weak, according to Freddie Mac. The government-sponsored enterprise said its primary mortgage market survey showed the average rate for a 30-year, fixed mortgage declined to 4.87% for the week ending Thursday from 4.95% a week earlier. The average rate for a 15-year, fixed mortgage decreased to 4.15% from 4.22% the prior week, according to the Freddie Mac survey. Interest rates are slightly lower than a year earlier yet remain higher than the 2010 average of 4.7% for the 30-year, fixed mortgage that was the lowest in more than 50 years. Freddie Mac chief economist Frank Nothaft said rates for 30-year, fixed mortgages are almost 0.2 percentage points below this year’s high set three weeks ago. “However, housing demand still remains weak. New home sales in January were near record lows dating back to 1963 when the data began, according to the Census Bureau,” Nothaft said. “Similarly, pending sales of existing homes fell for the second consecutive month in January.” He cited the recent report from the National Association of Realtors showing pending homes sales fell 2.8% for the first month of the year. In early December, Nothaft said he expects rates on a 30-year, fixed mortgage to remain below 5% throughout 2011, as the economic recovery accelerates. Freddie Mac said the average five-year, adjustable-rate mortgage slid to 3.72% this week from 3.80% a week earlier and is down from 4.11% a year ago. The average rate for a one-year, ARM fell to 3.23% from 3.40% a week ago. The rate is down from 4.27% at this time in 2010. Write to Jason Philyaw.