WASHINGTON (AP) — A key long-term U.S. mortgage rate dipped this week, the second drop after a large increase two weeks ago.

Mortgage company Freddie Mac said Thursday the nationwide average for a 30-year loan slipped to 4.19 percent from 4.20 percent last week. The average for a 15-year mortgage, a popular choice for people who are refinancing, was unchanged at 3.36 percent.

The 30-year rate is down from 4.53 percent at the start of the year. Rates have fallen even though the Federal Reserve has been trimming its monthly bond purchases, which are intended to keep long-term borrowing rates low. The purchases are set to end next month.

Mortgage rates often follow the yield on the 10-year Treasury note. The 10-year note traded at 2.41 percent at midday Thursday, down sharply from 2.57 percent a week earlier.

The decline in the 30-year rate comes after sales of existing homes fell in August. Investors retreated from real estate and first-time buyers remained scarce, according to a report last week from the National Association of Realtors.

And fewer Americans signed contracts to buy homes in August, suggesting that sluggish sales could continue. The Realtors group said Monday that its seasonally adjusted pending home sales index fell 1 percent.

By contrast, the Commerce Department said last week that sales of newly constructed homes surged in August, to the fastest sales pace since May 2008.

To calculate average mortgage rates, Freddie Mac surveys lenders across the country between Monday and Wednesday each week. The average doesn't include extra fees, known as points, which most borrowers must pay to get the lowest rates. One point equals 1 percent of the loan amount.

The average fee for a 30-year mortgage fell to 0.4 point from 0.5 point last week. The fee for a 15-year mortgage remained at 0.5 point.

The average rate on a five-year adjustable-rate mortgage fell to 3.06 percent from 3.08 percent. The fee rose to 0.5 point from 0.4 point a week ago.

For a one-year ARM, the average rate dipped to 2.42 percent from 2.43 percent. The fee held at 0.4 point.