NEW YORK (Reuters) - U.S. single-family home prices rose less than expected on an annual basis in May, and were down from the prior month, a survey showed on Tuesday.

The S&P CoreLogic Case-Shiller composite index of 20 metropolitan areas rose 5.2 percent in May on a year-over-year basis, retreating from the 5.4 percent climb in the prior month and short of the estimate for a 5.5 percent increase from a Reuters poll of economists.

"Overall, housing is doing quite well," said David M. Blitzer, managing director and chairman of the index committee at S&P Dow Jones Indices.

"In addition to strong prices, sales of existing homes reached the highest monthly level since 2007 as construction of new homes showed continuing gains."

Prices in the 20 cities fell 0.1 percent in May from April on a seasonally adjusted basis, the survey showed, matching expectations for a decline of 0.1 percent.

On a non-seasonally adjusted basis, prices increased 0.9 percent from April.

Home prices in three U.S. cities - Denver, Seattle and Portland, Oregon - showed the highest year-over-year gains, the survey showed.

(Reporting by Chuck Mikolajczak; Editing by Meredith Mazzilli)