The Conference Board's forward-looking leading economic index (LEI) rose 0.4% after April's 0.1% decline was revised to no change.
The financial components made the largest positive contributions to the index, more than offsetting the substantial negative contributions from stock prices and building permits, the board said.
The LEI has been on an uptrend for more than a year but its six-month growth rate up to May has continued to moderate, the board said.
"The index points to continued, though slower, U.S. growth for the rest of this year," said Bart van Ark, chief economist of The Conference Board.
He said public debt and deficits weighed heavily on growth prospects in the United States as well as Europe.
"We project a serious slowdown in European growth in 2011, which could further weaken the U.S. outlook."
The board's coincident index, a measure of current economic activity, rose 0.4% in May, following the same increase in April and a 0.3% gain in March.
Copyright Agence France-Presse, 2010