The U.S. housing market is still in recession, with prices all over the country declining and testing 2009 trough levels, according to the latest S&P/Case-Shiller Home Price Index.

The January Case-Shiller report released today showed that in 11 of the 20 cities surveyed, prices dropped below lows forged in 2009 following the bursting of a real estate bubble that peaked in 2006. Another month of declines adds to a trend many analysts suggest will continue.

Last month, Yale University’s Prof. Robert Shiller said the housing market is “vulnerable” in an assessment he conceded might be overly optimistic. He argued that the market’s strength since bouncing off its 2009 lows was largely linked to government tax credits aimed at creating demand for homes. Since they expired last summer, price declines have resumed.

The U.S. housing market is at the center of a credit crisis that sent the U.S. economy into perhaps its worst slowdown since the 1930s. Real estate remains a crucial element to a lasting recovery, which is why some analysts fret that renewed declines in prices are a bad omen for the whole economy.

“Keeping with the trends set in late 2010, January brings us weakening home prices with no real hope in sight for the near future,” David Blitzer, chairman of the index committee at Standard & Poor’s, said in the report. “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,” Blitzer added, referring to housing.

Home prices in January were at their lowest levels since mid-2003.

Prices in all cities except Washington, D.C., which inched up a meager 0.1 percent, fell in January. Also, prices in many of those cities dropped below bottoms forged in early 2009, as noted above.

Both the 10-City and 20-City composites that make up the Case-Shiller data series also slid further in January, marking the sixth consecutive month of declines.

The composites now sit only slightly above their 2009 trough. In broader perspective, they have fallen almost 32 percent since they peaked in mid-2006.

“A few months ago, we defined a double-dip for home prices as seeing the 10- and 20-City composites set new post-peak lows,” Blitzer said. “At this point, we are not too far off, and that is what many analysts are seeing with the sales, starts and inventory data too.”

In 11 of the 20 cities surveyed, prices set new lows for the cycle. In some cases, such as in Cleveland, Detroit, Las Vegas and now Atlanta, home prices are the lowest they’ve been in more than 11 years.

Washington, D.C., in contrast, “appears to be the only market that has weathered the recent storm,” Blitzer said in the report. The city has not only managed to post a month-on-month gain in January but, on an annual basis, it has gained 3.6 percent in the last year. Also, it remains a relatively healthy 10.7 percent above its 2009 trough level.

“It ranks No. 1 among the 20 markets, as its average value is almost 85 percent above its January 2000 level,” Blitzer noted.

San Diego is the only other city that managed to post a positive year-on-year reading of 0.1 percent, barely holding on to any gains it had made in the past 12 months.