WASHINGTON — Orders for airplanes, appliances and other long-lasting durable goods surprisingly dropped sharply last month.

Durable-goods orders dropped 4.3 percent in December after a downwardly revised 2.6 percent increase the previous month, the Commerce Department said Tuesday. Last month’s decrease was the largest since an 8.1 percent drop in July and marked the second decline in three months.

Economists had expected orders to increase about 1.6 percent in December.

Orders for durable goods are a key sign of future manufacturing activity. December’s drop came amid some other reports showing economic growth might have slowed instead of accelerated at the end of last year.

Sales of new homes fell 7 percent in December, the Commerce Department reported Monday. New orders for civilian aircraft and parts were a big factor in the transportation decline, falling 17.5 percent.