Single-family house prices, which through most of the past 12 months were showing healthy year-over-year and month-to-month gains, began to cool in March, according to the S&P/Case-Shilller Home Price Indices.

The Indices, released Tuesday morning, showed a drop of 0.4% in the 10-City Composite Index and a 0.5% drop in the 20-City Index from Februray to March and also showed a 3.2% drop in the U.S. National Index for the first quarter of 2010 compared to the fourth quarter of 2009. The national index, which stood at 131.81 at quarter's end, was down 1% from the third quarter of 2009 but remained 2% above its level at the end of 2009's first quarter.

Nationally, home prices were back to Spring, 2003 levels at the end of March.

"The housing market may be in better shape than this time last year; but, when you look at recent trends there are signs of some renewed weakening in home prices," said David M. Blitzer, chairman of the Index Committee at S&P. "In the past several months we have seen some relatively weak reports across many of the markets we cover," he continued."It is especially disappointing that the improvement we saw in sales and starts in March did not find its way to home prices.Now that the tax incentive ended on April 30th, we don't expect to see a boost in relative demand."

Not seasonally adjusted, thirteen metro areas and the two composites saw their prices drop in March over February. Boston, a 14th, was flat. Nearly all sequential gains occurred in the West and Texas (Dallas +0.4% to 115.74; Denver +0.6% to 125.31; San Diego +1.5% to 160.22; San Francisco +1.5% to136.74 and Seattle +0.1% to 143.73.) The exception was Cleveland, which was up 1.8% sequentially.The two Composites were down for the sixth consecutive month.

Half the measured markets still showed year-over-year gains: Boston, at 151.42, was up 3.8%; Cleveland at 103.32, was up 6.7%; Dallas up 3%; Denver up 4.1%; Los Angeles, at 170.62, up 6%; Minneapolis, at 116.66, up 6.5%; Phoenix, at 109.52, up 2.4%; San Diego up 10.8%; San Francisco up 16.2%; and Washington D.C., at 175.28, up 5.6%.

Down markets both sequentially and year-over-year included Atlanta, 103.74, down 1.8% and 1.3% respectively; Charlotte, 114.74, down 1.1% and 3.9%; Detroit, 67.66, down 4.1% and 4.6%; Las Vegas, 102.58, down 0.8% and 12%; Miami, 146.15, down 0.9% and 1.7%; New York, 169.42, down 0.7% and 2.4%; Portland, 143.61, down 0.1% and 2.8%; and Tampa, 136.46, down 0.1% and 3.5%.

The indices are based on a value of 100 set in January of 2000.