* Earnings season begins this week
* NPS Pharma climbs; to be acquired by Shire
* Energy shares fall as oil tumbles
* Indexes off: Dow 0.7 pct, S&P 0.9 pct, Nasdaq 0.9 pct (Updates to late afternoon trading, changes byline)
By Caroline Valetkevitch
NEW YORK, Jan 12 (Reuters) - U.S. stocks fell on Monday, led by a decline in energy shares as oil prices tumbled about 5 percent and concern grew ahead of the start of corporate earnings season.
Oil prices extended their recent free-fall, with Brent falling 5.3 percent to settle at $47.43 and U.S. crude dropping 4.7 percent to $46.07. Goldman Sachs slashed its short-term price forecasts and Gulf producers showed no signs of curbing output.
The S&P energy index, down 3.1 percent, was the day's worst-performing S&P 500 sector.
"It's crude-related. That's caused more selling. There's a lot of confusion and concern about the impact of energy prices," said Tim Ghriskey, chief investment officer of Solaris Group in Bedford Hills, New York.
Fourth-quarter earnings estimates have fallen in recent months as forecasts for energy profits have dropped sharply. Earnings are expected to increase by just 4 percent over the year-ago period, according to Thomson Reuters data.
Alcoa is scheduled to post quarterly earnings after the closing bell, while financials JPMorgan Chase, Wells Fargo, Goldman Sachs and Citigroup due to report later in the week. Dow component Intel Corp is expected to post earnings on Thursday.
"What everybody is concerned about is what managements are going to say about crude oil and about global economies," Ghriskey said.
At 2:51 p.m., the Dow Jones industrial average fell 122.7 points, or 0.69 percent, to 17,614.67, the S&P 500 lost 19.26 points, or 0.94 percent, to 2,025.55 and the Nasdaq Composite dropped 43.91 points, or 0.93 percent, to 4,660.16.
Since hitting a record high on Dec. 29, the S&P 500 has fallen about 3 percent on concerns about plunging oil prices, global economic weakness and Greece's potential exit from the euro zone.
Tiffany & Co shares slumped 14.4 percent after the upscale jeweler cut its full-year profit forecast, citing a disappointing holiday shopping season.
NPS Pharmaceuticals shares jumped 8.2 percent and were among the most active on Nasdaq after Shire Plc agreed to acquire the company for $5.2 billion. U.S.-listed shares of Shire slipped 1.5 percent.
Declining issues outnumbered advancing ones on the NYSE by 1,956 to 1,092, for a 1.79-to-1 ratio; on the Nasdaq, 1,716 issues fell and 1,010 advanced for a 1.70-to-1 ratio.
The S&P 500 was posting 29 new 52-week highs and 23 new lows; the Nasdaq Composite was recording 70 new highs and 78 new lows. (Additional reporting by Chuck Mikolajczak; editing by Bernadette Baum, Nick Zieminski and Meredith Mazzilli)