WASHINGTON (AP) — Orders for long-lasting U.S. manufactured goods dropped in August with weakness in a key category that tracks business investment plans. The underlying demand for manufactured goods has been weaker this year as a strong dollar and China's economic slowdown have dragged down demand for American exports and big declines in oil prices have resulted in cutbacks in investment by energy companies. [...] economists said the 2 percent August decline overstated the weakness in manufacturing because much of the drag last month came from a huge 19.3 percent fall in orders for defense equipment, an extremely volatile category. The overall economy, as measured by the gross domestic product, grew at an annual rate of 3.7 percent in the April-June quarter, an estimate that will be revised on Friday.