WASHINGTON — Fixed mortgages were mostly flat this week after hitting their lowest levels in decades. But few Americans are capitalizing on them. The average rate on the 30-year fixed mortgage stayed at 4.22 percent for the second straight week, Freddie Mac said Thursday. The rate hit 4.15 percent two weeks ago, the lowest level on records dating to 1971.

The average rate on the 15-year fixed mortgage, a popular refinancing option, fell to 3.39 percent from 3.44 percent. Two weeks ago, it reached 3.36 — the lowest rate on records dating to 1991 and likely the lowest ever, according to economists.

Mortgage rates typically track the yield on the 10-year Treasury note. Yields rose this week as investors shifted money back to a more stable stock market.

Low rates have done little to revive a weak housing market. Mortgage applications to purchase a home fell to 15-year lows last month. High unemployment, falling home prices and weaker economy have left many people hesitant about home buying.