U.S. stocks dropped Friday as concerns about slowing economic growth persisted, causing investors to sell shares of bellwether companies such as plane maker Boeing Co. and leaving all three major indexes in the red for the week.

The Standard & Poor's 500 index and the Nasdaq had their biggest weekly drops since July. Trading was light ahead of the three-day Christmas weekend.

Durable goods orders, excluding volatile transportation orders, fell unexpectedly in November, a government report showed. It was the second consecutive monthly drop in durables orders excluding transportation and the fourth decline in the last five months.

"One of the most important variables next year is capital spending, and this gives you some insight into capital spending intentions. Frankly, I think it's going to be disappointing," said Michael Metz, chief investment strategist at Oppenheimer & Co. in New York.

The Dow Jones industrial average fell 78.03 points, or 0.63 percent, to end at 12,343.22. The Standard & Poor's 500 Index was down 7.54 points, or 0.53 percent, at 1,410.76. The Nasdaq Composite Index was down 14.67 points, or 0.61 percent, at 2,401.18.

For the week, the Dow ended down 0.8 percent, the S&P 500 ended down 1.1 percent and the Nasdaq closed down 2.3 percent.

Boeing shares were among those leading declines, dropping 1.3 percent, or $1.18, to $88.76. It was the biggest drag on the Dow.

Shares of chemical maker DuPont dropped 0.8 percent, or 41 cents, to $48.57.

The key Dow Jones transportation average dropped 0.7 percent.

Shares in software maker Microsoft Corp., among stocks often viewed as a bellwether of capital spending, was the biggest drag on the S&P 500 and one of the biggest drags on the Nasdaq. Microsoft fell 1.1 percent, or 34 cents, to $29.64.

Excluding transportation orders, which are heavily skewed by aircraft, durable goods orders fell by 1.1 percent, the Commerce Department report showed. Orders had been expected to gain 1.0 percent when transportation orders were stripped out.

The data followed a Thursday report that showed the U.S. economy in the third quarter grew at a slower rate than earlier estimated, sparking concern that economic growth may be slowing faster than expected.

Recent weakness in prices of commodities such as copper, which are seen as indicators of economic growth, added to negative sentiment on the economic outlook, traders said.

Copper for March delivery fell 2.65 cents to end at $2.8540 a lb on the New York Mercantile Exchange's COMEX division.

Shares of Qualcomm Inc. fell 1.9 percent, or 73 cents, to $37.81 after the designer of microchips for mobile telephones lowered its first-quarter profit forecast, citing higher legal costs and a deferred payment from a customer.

JP Morgan analysts cut their rating on the stock to "underweight."

In other economic news, the government reported that core prices, excluding volatile food and energy costs, were flat in November after rising 0.2 percent in October.

Trading was light on the New York Stock Exchange, with about 990 million shares changing hands, well below last year's daily average of 1.61 billion, while on Nasdaq, about 1.32 billion shares traded, below last year's daily average of 1.80 billion.

Declining stocks outnumbered advancing ones by a ratio of 5 to 3 on the NYSE and by 17 to 13 on Nasdaq.