* Earnings season begins this week
* NPS Pharma climbs; to be acquired by Shire
* Energy shares fall as oil tumbles
* Indexes off: Dow 0.6 pct, S&P 0.8 pct, Nasdaq 0.8 pct (Updates to 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 fell further while concern grew ahead of the start of corporate earnings season.
Oil prices continued their downward march and weighed on equities. Brent was down more than 5 percent to $47.44 and U.S. crude down 4.6 percent at $46.13, as Goldman Sachs slashed its short-term price forecasts and Gulf producers showed no signs of curbing output.
The S&P energy index, the day's worst-performing S&P 500 sector, was down 2.7 percent.
"People are getting a little bit ahead of this selloff in anticipation of fourth-quarter earnings announcements and more worry about the large multinationals and what they are going to say about demand globally, as well as the impact of the dollar," said Keith Bliss, senior vice-president at Cuttone & Co in New York.
Fourth-quarter earnings estimates have fallen in recent months as forecasts for energy profits have dropped. 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, with 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.
At 1:38 p.m., the Dow Jones industrial average fell 100.63 points, or 0.57 percent, to 17,636.74, the S&P 500 lost 16.67 points, or 0.82 percent, to 2,028.14 and the Nasdaq Composite dropped 39.57 points, or 0.84 percent, to 4,664.50.
Since hitting a record high on Dec. 29, the S&P 500 has fallen about 2.6 percent on concerns about global growth, Greece's potential exit from the euro zone, and falling oil prices.
Tiffany & Co shares slumped 11.6 percent to $91.42 after the upscale jeweler cut its full-year profit forecast, citing a disappointing holiday shopping season.
NPS Pharmaceuticals shares jumped 8.2 percent to $45.35 after Shire Plc agreed to acquire the company for $5.2 billion. U.S.-listed shares of Shire slipped 1.5 percent to $214.23.
Declining issues outnumbered advancing ones on the NYSE by 1,982 to 1,029, for a 1.93-to-1 ratio on the downside; on the Nasdaq, 1,685 issues fell and 1,010 advanced for a 1.67-to-1 ratio favoring decliners.
The benchmark S&P 500 index was posting 28 new 52-week highs and 22 new lows; the Nasdaq Composite was recording 65 new highs and 75 new lows (Additional reporting by Chuck Mikolajczak; editing by Bernadette Baum, Nick Zieminski and Meredith Mazzilli)