WASHINGTON (Reuters) - U.S. mortgage rates fell this week for the first time in more than a month amid signs of slowing economic activity, but remain too high to provide a significant boost to the housing market.

The average rate on the popular 30-year fixed-rate mortgage was down to 7.09% as of May 9, from 7.22% last week, ending five straight weekly increases, mortgage finance agency Freddie Mac said in a statement on Thursday. It averaged 6.35% during the same period a year ago.

The average rate on the 15-year fixed-rate mortgage fell to 6.38% from 6.47% last week. That compared to an average of 5.75% a year ago. The decline in mortgage rates coincides with a drop in the 10-year Treasury yield following recent data showing a moderation economic and job growth.

"An environment where rates continue to hover above seven percent impacts both sellers and buyers," said Sam Khater, Freddie Mac's chief economist.

"Many potential sellers remain hesitant to list their home and part with lower mortgage rates from years prior, adversely impacting supply and keeping house prices elevated. These elevated house prices add to the overall affordability challenges that potential buyers face in this high-rate environment."