WASHINGTON – Mortgage rates for 30-year loans plunged to the lowest level in more than eight months.

The average for a 30-year fixed loan dropped to 4.39 percent in the week ended yesterday from 4.55 percent, according to Freddie Mac. The average 15-year fixed-loan rate decreased to a record 3.54 percent from 3.66 percent.

The decline followed a slide in yields for 10-year Treasury notes, which touched the lowest level since November on Wednesday as concern grew that the economy is slowing.

The rate for a 30-year fixed mortgage is the lowest since the week ended Nov. 18, when it also was 4.39 percent.

It fell earlier in November to 4.17 percent, the lowest in Freddie Mac records dating to 1971.

The low borrowing costs have done little to boost home sales as banks tighten lending standards, the unemployment rate sticks above 9 percent, and a glut of foreclosed properties drag down prices.

About 22.7 percent of homeowners with mortgages were underwater in the first quarter, meaning they owe than their properties are worth, according to CoreLogic Inc.