Caterpillar Inc said growth in dealer sales of its heavy equipment slowed in the three months ended July, particularly in North America, reinforcing concerns about the struggling U.S. economy.

The world's largest maker of construction equipment said on Thursday that dealer sales -- an indicator of future revenue -- rose 35 percent worldwide over the past three months, a slower rate than the 45 percent growth reported in July.

Caterpillar shares were down 4.7 percent at $83.56 on Thursday morning, exceeding the 4.1 percent drop in the S&P 500 Index. <.SPX> Over the past year, Caterpillar shares have risen about 26 percent, outpacing the 10 percent climb of the Dow Jones industrial average <.DJI>.

Growth in North America slowed most dramatically -- to 27 percent from 50 percent -- and growth in the Asia-Pacific region dipped to 20 percent from 28 percent. Latin America was the one area to report an acceleration, with sales growth rising 1 point to 52 percent.

The report, which came in a filing with the U.S. Securities and Exchange Commission, marked the third straight decline in the growth rate from the most recent peak of a 66 percent rise in dealer sales for the three months ended in April.

Caterpillar, whose competitors include Japan's Komatsu Ltd <6301.T> and South Korea's Doosan Infracore Co Ltd <042670.KS>, warned investors last month that economic growth in the United States and other developed economies had been slower than expected this year, and also warned of signs of sagging demand in China, the world's fastest-growing major economy.

A report by the American Institute of Architects released on Wednesday also suggested nonresidential construction activity was slowing down in the United States. The slump in building homes and other buildings has contributed to the nation's persistent high unemployment rate by reducing demand for blue-collar workers in the construction trade.

(Reporting by Scott Malone, editing by Matthew Lewis)

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