WASHINGTON (AP) — U.S. home prices fell for a third straight month in nearly all cities tracked by a major index. The declines show that most homeowners are not reaping the benefits from some signs of an improving housing market.

Prices dropped in November from October in 19 of the 20 cities tracked, according to the Standard & Poor's/Case-Shiller home-price index released Tuesday. The steepest declines were in Atlanta, Chicago and Detroit. Phoenix was the only city to show an increase.

The declines partly reflect the typical fall slowdown after the peak buying season.

Still, prices fell in 18 of the 20 cities in November compared to the same month in 2010. Only Washington and Detroit posted year-over-year increases.

Prices in Atlanta, Las Vegas, Seattle and Tampa fell to their lowest points since the housing crisis began. And prices have fallen 33 percent nationwide since the housing bust, to 2003 levels.

"The trend is down and there are few, if any, signs in the numbers that a turning point is close at hand," said David M. Blitzer, chairman of the S&P's index committee.

The Case-Shiller index covers half of all U.S. homes. It measures prices compared with those in January 2000 and creates a three-month moving average. The November data are the latest available.

Home values remain depressed despite some hopeful signs at the end of last year.

Sales of previously occupied homes rose in the last three months. Homebuilders are more optimistic after seeing more people express interest in buying this year. And home construction picked up in the final quarter of last year, which helped housing contribute to broader economic growth.

Home prices tend to follow sales, which are still below healthy levels. And a large number of vacant homes are sitting idle on the market, which means prices will likely stay unchanged for several years, said Paul Dales, senior U.S. economist at Capital Economics.

"The most likely scenario in the U.S. is that in 2012 prices will bob around a bit, with one month's gain being reversed the next month," Dales said. "But in general, over the next couple of years, house prices will do nothing more than remain broadly stable."

Dales said prices might not rise consistently until 2015. He said lower unemployment and better pay raises are essential to a full housing rebound.

Among other improvements needed:

— The supply of homes for sale must decline further. The inventory fell in November to a seven-month supply, although a healthy supply is about six months.

— Sales need to rise consistently and more first-time buyers must drive the increases. First-time buyers stay longer and invest in their homes, which helps neighboring home values rise.

— More young people and immigrants must buy. Declining immigration and a rise in renting has hampered home sales.

— More than a million homes at risk of foreclosure must be cleared from the market. Many are in limbo because a government investigation into questionable mortgage lending practices, which has dragged on for more than a year.

— Banks must further loosen lending requirements.

Conditions are improving for those in position to buy a home. Job growth is up, prices are down, mortgage rates are at record lows and rental prices have risen sharply since the housing bust.

Still, many people can't afford to buy or are unable to qualify for mortgage. Some people in position to buy are holding off, worried that prices could fall even further.

Many economists say the U.S. could be experiencing what similarly occurred in Britain in the 1990s, when it took four years for home prices to rise again after falling prices left homeowners with little financial equity in their homes.