Home prices in 20 major metropolitan areas fell 3.1 percent year-over-year in January, prompting Standard & Poor’s to declare “home prices off to a dismal start in 2011” in its latest S&P/Case-Shiller Home Price Indices report released today.

The 20-city composite index fell 1 percent in January compared to December, to 140.86. The indices have a base value of 100; a value above 100 indicates the appreciation rate of a typical home in the tracked markets since January 2000. Average home prices are back to the levels they were in the summer of 2003, the report said.

Out of the 20 markets tracked, 19 saw their index levels fall month-to-month in January, and the index in the remaining market, Washington, D.C., stayed essentially flat, with a 0.1 percent increase —  those numbers are not seasonally adjusted. The 20-city composite index has posted monthly declines for the past six months straight.

Only two of 20 cities showed year-over-year index gains in January: San Diego with a 0.1 percent increase, and Washington, D.C., with a 3.6 percent increase. Phoenix and Detroit saw the biggest year-over-year declines: 9.1 percent and 8.1 percent, respectively.

The same 11 cities that “double-dipped” in the previous month’s report hit new lows in January: Atlanta; Charlotte; Chicago; Detroit; Las Vegas; Miami; New York; Phoenix; Portland, Ore.; Seattle and Tampa. Four cities — Atlanta, Cleveland, Detroit, and Las Vegas — have index levels below 100, indicating that average home prices there are below January 2000 levels.

“Keeping with the trends set in late 2010, January brings us weakening home prices with no real hope in sight for the near future,” said David M. Blitzer, chairman of the Index Committee at Standard & Poor’s, in a statement.

“The housing market recession is not yet over, and none of the statistics are indicating any form of sustained recovery. At most, we have seen all statistics bounce along their troughs; at worst, the feared double-dip recession may be materializing.”

When the 10-city and 20-city composite indices set new post-peak lows, home prices will have double-dipped, Blitzer added.

“The 10-city composite is still 2.8 percent above and the 20-city is 1.1 percent above their respective April 2009 lows, but both series have moved closer to a confirmed double-dip for six consecutive months. At this point we are not too far off, and that is what many analysts are seeing with sales, starts and inventory data too,” he said.

The 20-city composite index has fallen 31.8 percent from its peak in June and July 2006.