Orders for long-lasting manufactured goods increased last month by the largest amount in eight months, the U.S. government said Friday, although a key category that tracks business investment plans dropped for a seventh straight month. The Commerce Department reported that orders for durable goods rebounded 4 percent in March after having fallen 1.4 percent in February. The rebound was led by a significant jump in demand for commercial aircraft. Outside of that transportation category, orders were down for a sixth straight month. There also was a 0.5 percent drop in demand in the category that serves as a proxy for business investment plans. The decline followed a 2.2 percent drop in February. This important category has been down for seven consecutive months. Demand for commercial aircraft climbed 30.6 percent in March after a 2.2 percent decline in February. Orders for motor vehicles rose 5.4 percent, and the overall transportation category expanded 13.5 percent. Excluding transportation, the weakness was widespread with orders down 0.2 percent. Demand for primary metals such as steel moved down 0.2 percent, while orders for machinery dropped 1.5 percent. Demand for communications equipment fell 5.3 percent. Orders for computers rose and related equipment gained 11 percent in one of the few areas of strength in March. Economists say that overall economic growth slowed to between 1 percent and 1.5 percent in the January-to-March quarter. They have high hopes for a rebound to growth of around 3 percent for the rest of this year.