* China may tighten cash supply to address inflation risks
* Corning jumps, Samsung unit may become largest shareholder
* Caterpillar falls after results, Boeing up
* Indexes off: Dow 0.3 pct, S&P 0.5 pct, Nasdaq 0.7 pct
NEW YORK, Oct 23 (Reuters) - U.S. stocks fell on Wednesday after four straight days of record highs on the S&P 500, amid concern over tightening financial conditions in China and weakness in European banks.
Two Dow components highlighted a mixed earnings picture on Wall Street, with Caterpillar shares down 5.5 percent after cutting its full-year earnings forecast, and Boeing up 5.9 percent after raising its outlook for the year.
Major global equity markets weakened as China's primary short-term money rates rose on concern the People's Bank of China may tighten its cash supply to address inflation risks, a move that could hurt growth in the world's second-largest economy.
Further hurting sentiment, the European Central Bank said it would put top euro zone banks through rigorous tests next year to build confidence in the sector. However, some analysts say if the review reveals unexpectedly large problems it could backfire by undermining the confidence it aims to bolster.
The S&P financial sector index fell 0.8 percent.
"With Caterpillar cutting its outlook for the year and concerns over China slowing against a backdrop of a market at a record, some people just decided to ring the cash register and take some profits," said Eric Kuby, chief investment officer at North Star Investment Management Corp in Chicago.
He said the selling is "orderly" and indicates more a pause than nervousness on the part of investors.
The Dow Jones industrial average fell 40.08 points or 0.26 percent, to 15,427.58, the S&P 500 lost 7.89 points or 0.45 percent, to 1,746.78 and the Nasdaq Composite dropped 27.362 points or 0.7 percent, to 3,902.204.
The S&P 500 closed Tuesday at 1,754.67 after climbing earlier in the day to near 1,760. Its 23 percent gain on the year to Tuesday was just shy of its 23.5 percent advance in 2009, the index's best year in the past decade.
Shares of Caterpillar Inc fell 5.5 percent to $84.25 after the mining and construction equipment company posted a lower-than-expected quarterly profit and cut its full-year forecast again.
Boeing Co reported a rise in adjusted profit in the third quarter and raised its full-year forecast, sending its shares up 5.9 percent to $129.73.
A unit of Samsung Electronics could become the biggest shareholder of Corning Inc, the maker of scratch-resistant Gorilla Glass used in many mobile gadgets. Corning shares jumped 13.8 percent to $17.47.
Broadcom, programmable chipmaker Altera and radio frequency chipmaker RF Micro Devices on Tuesday joined Intel and Texas Instruments on a list of semiconductor companies that have unveiled underwhelming quarterly forecasts over the past week.
Broadcom shares fell 8 percent to $24.97, Altera lost 12 percent to $32.81 and RF Micro lost 10 percent to $5.55.
Shares of Cree Inc fell 18 percent to $60.89 after the maker of light-emitting diodes forecast current-quarter earnings below analysts' estimates.