The Standard & Poor's/Case-Shiller index released Tuesday showed prices dropped in October from September in 19 of the 20 cities tracked.
Prices in a majority of cities declined for the second straight month, reflecting the typically fall slowdown after the peak buying season. Prior to that, prices had risen for five consecutive months in at least half of the cities tracked.
Home prices are softening despite some modest progress in the depressed housing market.
Residential construction is likely to add to U.S. economic growth in 2011, the first time that has happened in four years. Still, that's mainly because apartments are being built almost twice as fast as two years ago - reflecting a surge in renting and weaker home sales.
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 monthly data are not seasonally adjusted.
Atlanta, Detroit and Minneapolis posted the biggest monthly declines. Prices in Atlanta and Las Vegas fell to their lowest points since the housing crisis began. Prices rose in Phoenix after three straight monthly declines.
David M. Blitzer, chairman of S&P's index committee, said steep price drops in cities such as Atlanta, Chicago, Cleveland, Detroit and Minneapolis were particularly worrisome because their gains earlier this season were so strong.
"Atlanta and the Midwest are regions that really stand out in terms of recent relative weakness," Blitzer said. "These markets were some of the strongest during the spring/summer buying season."
Americans are reluctant to purchase a home more than two years after the recession officially ended. High unemployment and weak job growth have deterred many would-be buyers. Even the lowest mortgage rates in history haven't been enough to lift sales.
Sales of previously occupied homes are barely ahead of 2008's dismal figures - the worst in 13 years. And sales of new homes this year will likely be the worst since the government began keeping records a half century ago.
Prices are also certain to fall further once banks resume millions of foreclosures. They have been delayed because of a yearlong government investigation into mortgage lending practices.
Home prices had stabilized in coastal cities over the past six months, helped by a rush of spring buyers and investors. But this year, prices in many cities, including Cleveland, Detroit, Las Vegas, Phoenix and Tampa, have reached their lowest points since the housing bust more than four years ago.
Foreclosures and short sales - when a lender accepts less for a home than what is owed on a mortgage - are selling at an average discount of 20 percent.