US STOCKS-Wall St marks worst day in 3 months as Q4 begins

* National factory activity data disappoint investors

* Jobless claims rise in latest week

* Tech, bank shares among hardest hit

* Dow off 2.1 pct, S&P off 2.6 pct, Nasdaq off 3.1 pct

* For up-to-the-minute market news, click [STXNEWS/US] (Updates to close)

By Caroline Valetkevitch

NEW YORK, Oct 1 (Reuters) - The Dow and S&P 500 suffered their worst one-day fall in three months on Thursday after economic reports fueled fears about the recovery's strength.

The pullback occurred a day after stocks ended the third quarter with strong gains, with the Dow and S&P each up 15 percent from the previous quarter.

Cyclical stocks, which are sensitive to the economy's cycles, were among the worst performers, including technology and bank shares. The KWB bank index <.BKX> dropped 5 percent while an index of semiconductors <.SOXX> fell 4.8 percent. Airlines also fell sharply, with an airline index <.XAL> down 8.3 percent.

The Institute for Supply Management's index of national factory activity declined in September from August's reading, and although the latest reading still indicated growth, it was sharply below economists' forecast in a Reuters poll. For details, see [ID:nN01395512] Please see graphic: http://graphics.thomsonreuters.com/109/US_ISMGDP1009.gif

Data on jobless claims also was worse than expected.

"There was disappointment from the ISM this morning. It missed expectations," said Mike O'Rourke, chief market strategist at BTIG in New York.

"With the last quarter ending, a lot of people were holding stuff up for window dressing and now you're seeing profit-taking," he added. "We've had a tremendous run up."

Analysts said the news added to anxiety ahead of Friday's September jobs report from the government, the month's biggest data release.

The Dow Jones industrial average <.DJI> tumbled 203.00 points, or 2.09 percent, to end at 9,509.28. The Standard & Poor's 500 Index <.SPX> slid 27.23 points, or 2.58 percent, to 1,029.85. The Nasdaq Composite Index <.IXIC> lost 64.94 points, or 3.06 percent, to 2,057.48.

It was the third straight day of declines for stocks and the Nasday's worst fall since June 22, just before the market suffered a modest pullback.

All 30 Dow components finished in the red, with the Dow's biggest decliners including JPMorgan Chase & Co , down 5.6 percent at $41.37, and Boeing Co , down 3.8 percent at $52.11.

Bank of America Corp shares slipped 4.2 percent to $16.21 after Chief Executive Ken Lewis said he was retiring after months of being dogged by a series of government investigations into the company's acquisition of Merrill Lynch. The company did not name a successor. The news was announced late on Wednesday. [ID:nN30236559]

Heavy equipment maker Caterpillar , down 3.7 percent at $49.45, also ranked among the Dow's biggest decliners.

Among the Nasdaq's major losers were tech bellwethers Apple Inc , down 2.4 percent at $180.8599; Qualcomm Inc , down 5.1 percent at $42.70 and Microsoft , down 3.3 percent at $24.88.

The ISM's manufacturing reading fell to 52.6, below economists' forecast of 54.0, and August's 52.9.

The S&P 500, however, is still up 52.2 percent from its 12-year closing low on March 9. (Editing by Jan Paschal)