NEW YORK Tue Jul 29, 2014 9:23am

U.S. single-family home prices fell in May on a seasonally adjusted basis, falling short of expectations calling for a slight gain, a closely watched survey said on Tuesday.

The S&P/Case Shiller composite index of 20 metropolitan areas declined 0.3 percent in May on a seasonally adjusted basis. A Reuters poll of economists forecast a gain of 0.2 percent.

Non-seasonally adjusted prices rose 1.1 percent in the 20 cities, compared to an expectation of a 1.5 percent rise.

"Housing has been turning in mixed economic numbers in the last few months," said David Blitzer, chairman of the index committee at S&P Dow Jones Indices, said in a statement.

"Prices and sales of existing homes have shown improvement while construction and sales of new homes continue to lag."

Prices in the 20 cities rose 9.3 percent year over year, the slowest year-over-year gain since February 2013 and shy of expectations for a 10 percent climb.

The seasonally adjusted 10-city gauge fell 0.3 percent in May versus unchanged in April, while the non-adjusted 10-city index rose 1.1 percent in May compared to a 1 percent gain in April.

Year over year, the 10 city gauge rose 9.4 percent.