Home prices unexpectedly slipped in December but the annual rate of decline slowed, reinforcing the housing market's rocky road to recovery, Standard & Poor's/Case-Shiller indexes showed on Tuesday.

The S&P composite index of home prices in 20 metropolitan areas declined 0.2 percent in December, matching the dip in November, for a 3.1 percent annual drop.

A Reuters survey had forecast that prices would be unchanged for the month and down 3.2 percent annually.

The S&P/Case-Shiller U.S. national home price index, which covers all nine census divisions, fell 2.5 percent in the fourth quarter from the same time a year earlier. This measure, like the 20-city and 10-city indexes, have seen smaller annual declines all through 2009.

On a seasonally adjusted basis, the 20-city index rose 0.3 percent in December, S&P said, matching the November increase.

(Reporting by Lynn Adler)