WASHINGTON — Average rates on fixed mortgages have risen for a fourth straight week, but remain slightly above record lows.

Mortgage buyer Freddie Mac says the rate on the 30-year loan increased to 3.66 percent, up from 3.62 percent last week. Four weeks ago, it fell to 3.49 percent, the lowest since long-term mortgages began in the 1950s. The average on the 15-year fixed mortgage edged up to 2.89 percent, from 2.88 percent last week and a record low of 2.8 percent four weeks ago.

Low rates have lifted home sales this year. Housing will probably add to economic growth in 2012 for the first time in seven years. Sales of previously occupied homes rose 2.3 percent in July from June to a seasonally adjusted annual rate of 4.47 million, the National Association of Realtors reported this week.

New-home sales have been strengthening, too. Sales rose 3.6 percent in July to match a two-year high reached in May, the Commerce Department said Thursday.