As the U.S. housing market struggles to recover with unemployment hovering at 9% and Home prices dropping accross the country due to foreclosures, mortgage rates continue to decreased for a fourth week, sending borrowing costs to the lowest level since December. Freddie Mac reported that the average rate for a 30-year loan dropped to 4.63% in the week compared to last week's 4.71%. That is the lowest since the week ending Dec. 9, 2010. The 15-year rate slipped to 3.82% from 3.89% a week ago.Falling rates helped drive demand for mortgages last week and encouraged homeowners to reduce their monthly payments. The Mortgage Bankers Association's measure of refinancing rose 9% last week, the biggest increase in two months. Purchase applications climbed 6.7%. The average rate for a 30-year fixed loan is below where it was last year at this time, when it was 4.93% It fell to a record 4.17% in November.