* Wall Street coming off worst week of 2013
* Halliburton rallies after results
* Power-One soars after $1 billion purchase offer from ABB
* Indexes off: Dow 33 pct, S&P 0.25 pct, Nasdaq 0.11 pct
By Chuck Mikolajczak
NEW YORK, April 22 (Reuters) - U.S. stocks edged lower on Monday, as earnings from Caterpillar, Halliburton and other major companies pointed to more volatile trading ahead.
General Electric, down 2.1 percent to $21.29 and McDonald's Corp, off 1.2 percent to $98.66, extended losses from Friday after posting lackluster earnings. Both stocks were declining for the fourth straight day.
Wall Street is coming off a week of extreme volatility, with the CBOE Volatility index jumping 24 percent, the biggest weekly gain for the so-called fear index this year. The index was up 2.5 percent on Monday.
The swings were largely driven by weak corporate earnings and signs of slowing growth from China, which led to a steep drop in commodity prices. The week's decline fueled talk that the market's long anticipated pullback had arrived, though the S&P remains up nearly 9 percent on the year.
Caterpillar reported disappointing quarterly results and cut its 2013 profit forecast. Its stock advanced 0.6 percent to $80.92 after bullish comments from Chairman and Chief Executive Officer Doug Oberhelman.
Halliburton, the oil field services company, rose 2.6 percent to $38.19 after the company posted quarterly results and said it is in talks to settle private claims against it in a trial.
"This is all going to be very much a direction driven by earnings," said Peter Kenny, managing director at Knight Capital in Jersey City, New Jersey.
"The majors are only off 3 to 4 percent from the high but we have done that fairly efficiently and if earnings are any indication, there is going to be more choppy action ahead."
Earnings also due on Monday included Texas Instruments and Netflix Inc after the market's close. For the week, 168 companies in the S&P 500 are scheduled to report earnings.
With 104 S&P 500 components having reported through Friday, 67.3 percent of companies have topped profit expectations, according to Thomson Reuters data. Analysts expect earnings growth of 2.1 percent this quarter, up from expectations of 1.5 percent at the start of the month.
The Dow Jones industrial average dropped 48.66 points, or 0.33 percent, to 14,498.85. The Standard & Poor's 500 Index shed 3.90 points, or 0.25 percent, to 1,551.35. The Nasdaq Composite Index lost 3.48 points, or 0.11 percent, to 3,202.58.
Investors will be looking to the S&P 500's 50-day moving average of 1,544.74, which could serve as a level of market support. The index closed under that level for the first time this year on Thursday but rebounded above it on Friday.
The National Association of Realtors said existing-home sales edged down 0.6 percent last month to a seasonally adjusted annual rate of 4.92 million units. Economists polled by Reuters had expected home resales to rise to a 5.01 million-unit rate.
Power-One Inc soared 56.4 percent to $6.32 in after ABB agreed to buy the company for about $1 billion.