US STOCKS-Wall Street falls as investors book gains

* Microsoft falls after Goldman downgrade

* Dollar strength hurts commodity-related stocks

* Home sales, factory orders underscore weak economy

* Indexes off: Dow 1 pct, S&P 1.1 pct, Nasdaq 1.3 pct

* For up-to-the-minute market news see [STXNEWS/US] (Updates to late afternoon)

By Edward Krudy

NEW YORK, Oct 4 (Reuters) - U.S. stocks fell on Monday as disappointing economic data, combined with worries about euro zone debt, pushed investors away from riskier assets and sparked profit-taking after a recent rally.

Troubling economic news from Ireland, Portugal and Greece renewed concerns about the euro zone debts, hurting the euro currency and sending the safe-haven U.S. dollar higher. For details, see [ID:nN04116466].

That hit commodity prices and related stocks. The S&P materials index <.GSPM> led the decline, falling 1.7 percent.

Mark Luschini, chief investment strategist at Janney Montgomery Scott in Philadelphia, said that investors were using the renewed risk aversion to take profits after September's 9 percent run-up in the S&P 500.

"We're coming off exceptionally strong performance in the month of September, he said. "You probably have a little bit of an element of profit taking that was maybe accelerated by the disappointing data points this morning."

The Dow Jones industrial average <.DJI> fell 104.63 points, or 0.97 percent, at 10,725.05. The Standard & Poor's 500 Index <.SPX> lost 12.04 points, or 1.05 percent, at 1,134.20. The Nasdaq Composite Index <.IXIC> declined 30.73 points, or 1.30 percent, at 2,340.02.

Pending sales of previously owned U.S. homes indicated the housing market was stabilizing at a very low level, while new orders received by U.S. factories fell 0.5 percent in the same month.

Microsoft Corp was a drag on both the Dow and Nasdaq 100, dropping 2.3 percent to $23.83 after Goldman Sachs downgraded the software maker, citing a slow recovery in PC sales and competition from tablet computers, which do not include Windows software. [ID:nSGE6930CY].

The falling U.S. dollar pressured commodity-related stocks. Industrial materials shares fell, with U.S. Steel Corp off 3.9 percent to $42.92 and Alcoa down 3 percent to $11.8.

The Irish central bank said on Monday Ireland's economy will crawl to a virtual halt this year, while Greece forecast the economy will contract 2.6 percent next year after a 4.0 percent slump in 2010. Portuguese officials urged unity on austerity measures in the face of opposition.

The S&P 500 recently finished its best quarter in a year, although the index has been struggling to break out of the 1,130-1,150 range.

The index fell back below the the 61.8 Fibonacci retracement of its April to July pullback at 1,140 and moved back towards support at 1,130, a level the index struggled against, finally climbing above it in late September.

S&P 500 short-term technical indicators showed sell signals. The benchmark index's 10-day momentum line fell below zero, indicating a short-term trend reversal, while the trend lines of the moving average convergence-divergence (MACD) indicator crossed at oversold levels.

The third-quarter earnings season will begin unofficially this week with Alcoa's results on Thursday. Micron Technology Inc , PepsiCo Inc and Monsanto Co are also set to report this week. (Reporting by Edward Krudy; Editing by Kenneth Barry)