The average price of a single-family home fell again in November, with decreases in 19 of the 20 largest metropolitan areas during the month, according to the Standard & Poor’s/Case-Shiller index.

The ratings agency’s 20-city composite index and 10-city index both declined 1.3% from a month earlier. The larger, benchmark index drop 3.7% from November 2010 and the 10-city index for November was 3.6% lower than the year earlier.

S&P said both indices are one-third lower than the peak in the summer of 2006 and home prices are now at levels last seen in the middle of 2003.

Atlanta home prices for November were nearly 12% lower than the prior year, while Detroit at 3.8% and Washington with a 0.5% gain are the only metropolitan areas to post annual increases. Home prices in Atlanta, Las Vegas, Seattle and Tampa, Fla., all reached new lows in November, according to S&P/Case-Shiller.

“Despite continued low interest rates and better real GDP growth in the fourth quarter, home prices continue to fall,” said David Blitzer, chairman of the S&P index committee.

He said Phoenix, one of the hardest-hit areas in recent years, was the only MSA to post an increase in prices from October with a 0.6% gain.

“Annual rates were little better as 18 cities and both composites were negative,” Blitzer said. “The trend is down and there are few, if any, signs in the numbers that a turning point is close at hand.”

Analysts with Toronto-based Capital Economics agreed and said “there are still no signs that house prices are on the verge of turning around,” as the Case-Shiller indices fell for the seventh month in a row.

“But things should be different in six months’ time, when the recent rises in home sales will have helped to put a floor under prices,” the analysts said.

Write to Jason Philyaw.

Follow him on Twitter: @jrphilyaw.