* Indexes down: Dow 1.88 pct, S&P 1.91 pct, Nasdaq 1.74 pct (Updates prices)
By Sinead Carew
NEW YORK, Jan 5 (Reuters) - Energy shares led a broad decline on Wall Street on Monday in the wake of a drop in crude prices to fresh 5-1/2 year lows amid concerns economic problems elsewhere in the world could hurt the United States.
The S&P was set for its first four-day losing streak since December 2013 as crude oil futures prices dropped to their lowest since May 2009 amid a global supply glut and lackluster demand.
Russia's oil output hit a post-Soviet high last year, and Iraq's oil exports in December were highest since 1980. U.S. crude dipped below $50 a barrel for the first time since April 2009 and Brent fell 6 percent.
The euro fell to a near nine-year low against the dollar of $1.18605 on the EBS platform, tumbling on political uncertainty in Greece and fears of a possible Greek exit from the euro zone.
On top of the oil price impact on energy companies, Stephen Massocca, chief investment officer, Wedbush Equity Management LLC in San Francisco said investors were concerned about overseas economies, with a particular focus on Europe.
"We were at this elevated high at the end of December adding to the impetus for the decline on top of worldwide growth concerns and what's going on in energy. Those are the three big issues right now," he said.
The strength in the dollar was putting more pressure on dollar-denominated commodities. A measure of the greenback against a basket of major currencies hit its highest since December 2005.
"Multinationals will have their earnings decreased if they aren't fully hedged," said Rick Meckler, president of LibertyView Capital Management in Jersey City.
At 2:47 p.m., the Dow Jones industrial average fell 335.44 points, or 1.88 percent, to 17,497.55, the S&P 500 lost 39.29 points, or 1.91 percent, to 2,018.91 and the Nasdaq Composite dropped 82.12 points, or 1.74 percent, to 4,644.69.
The S&P 500 energy sector was down 4 percent, on track for its largest daily percentage decline since November 28. It fell almost 20 percent in the second half of last year. The health sector, the S&P's best performer on Monday was down 0.45 percent.
The S&P's worst performer was United Rental with a 10.7 percent decline, followed by Noble Energy, which was down 9.9 percent in afternoon trade.
One bright spot was Gilead Sciences Inc. Shares rose 2.6 percent after CVS Health Corp, one of the largest U.S. managers of drug benefits, said it will give Gilead's hepatitis C treatment preferred status and cover a competing treatment from AbbVie Inc only as an exception. AbbVie shares lost 2 percent.
Declining issues outnumbered advancing ones on the NYSE by 2,452 to 667, for a 3.68-to-1 ratio; on the Nasdaq, 1,998 issues fell and 755 advanced for a 2.65-to-1 ratio.
The benchmark S&P 500 index was posting 5 new 52-week highs and 6 new lows; the Nasdaq Composite was recording 48 new highs and 37 new lows.
Additional reporting by Rodrigo Campos and Chuck Mikolajczak; Editing by Bernadette Baum and Nick Zieminski