WASHINGTON — U.S. factories saw a surprisingly hefty increase in orders for big-ticket products in July, reflecting continued strength in export sales and a boost to business investment from the government's tax stimulus package.

Economists, however, remain worried that spreading economic weakness overseas and a rebound in the value of the dollar could spell an end to the export boom later this year.

The Commerce Department said Wednesday that orders for durable goods rose 1.3 percent last month, far above the slight 0.1 percent increase Wall Street had been expecting.

The July increase matched a 1.3 percent rise in June, which was revised up from an earlier reading of 0.8. The matching gains were the strongest since orders for durable goods, items expected to last at least three years, jumped 4.1 percent in December.