Orders for long-lasting US factory goods, excluding the volatile transportation category, fell in July for the fourth time in five months.
Analysts said the figures may be a sign that manufacturing is starting to falter.
The Commerce Department said orders for durable goods rose a seasonally adjusted 4.2% in July. But excluding aircraft and other transportation goods, orders dropped 0.4%.
Durable goods are items meant to last at least three years.
Today's data showed that aircraft orders soared 54%. Boeing, one of the biggest global aircraft manufacturers, received 260 orders last month, according to economists at IHS Global Insight, up from 21 in June.
Orders for core capital goods, a key measure of business investment plans, fell 3.4%. That is the biggest drop since November and the fourth decline in five months. Core capital goods include computers, industrial machinery and steel.
The steady decline in such orders suggests that companies are worried that the economy will slow and are reducing investment.
Europe's financial crisis has pushed that region to the brink of recession, threatening exports of US goods. Economies in China, India and Brazil are also growing more slowly.
The US economy is also at risk of going off a "fiscal cliff" at the end of the year. That is when tax increases and deep spending cuts will take effect unless Congress reaches a budget agreement.
This week, the Congressional Budget Office warned that if the fiscal crisis remained unresolved all next year, it would probably tip the US economy into a recession. Unemployment would rise to around 9% by late next year as a result of the spending cuts and tax increases, the CBO said. Unemployment is now 8.3%.
Some economists worry that companies may be postponing spending until the budget crisis is resolved. Manufacturing, a key source of growth earlier in the recovery, has already shown signs of weakness. Factory activity shrank for the second month in a row in July, according to a survey by the Institute for Supply Management, a trade group.
A separate report last week by the Federal Reserve painted a more positive picture - it said factory output rose last month, largely because of a jump in car production. That likely occurred because many car makers skipped their traditional summer shutdowns.
But economists worry that those gains in auto production will reverse in August.
The economy has shown modest improvement in recent weeks, but analysts do not expect growth to accelerate much. Growth may improve to an annual rate just below 2% in the three months from July to September, economists forecast.
