WASHINGTON - Average long-term U.S. mortgage rates slipped this week after they rose recently on expectations that the Federal Reserve may soon raise its key short-term interest rate. 

Mortgage buyer Freddie Mac said Wednesday the average rate on a 30-year fixed-rate mortgage slipped to 3.95 percent from 3.97 percent a week earlier. The key 30-year rate was nearly unchanged from its level of a year ago, 3.97 percent. But the average has increased over the past months from 3.76 at the end of October. 

The average on 15-year fixed-rate mortgages was unchanged at 3.18 percent from 3.20.