* Oil down almost 4 pct on renewed economic worries
* Corn, wheat and cocoa jump on supply worries
(Recasts, updates prices, market activity; changes byline and dateline, previously LONDON)
By Barani Krishnan
NEW YORK, Dec 15 (Reuters) - Oil, metals and grains futures settled mixed on Monday, extending the previous session's trend, as investors tried to balance economic worries with threats to supply in some key commodities.
"We're in a tug-of-war," Jim Ritterbusch, a veteran U.S. energy markets analyst, said, pointing to how oil prices, particularly, were fluctuating on contrasting fundamentals.
The Reuters-Jefferies CRB Index, a global commodities benchmark, ended half a percent down after last week's record gain of nearly 9 percent that marked its biggest rebound since a slump in commodities that began August.
U.S. crude oil futures settled nearly 4 percent down as falling demand for energy in China and losses in stock markets outweighed threats of oil production cuts from OPEC.
Copper futures fell over 1 percent in New York and London, also on demand concerns.
Bucking the downtrend was a 2 percent run-up in U.S. gold, which extended a rally from last week, as investors bought into the precious metal to hedge against a weaker dollar.
Corn and wheat surged as well on buying spurred by recent data suggesting smaller plantings for next year. Cocoa prices jumped 7 percent, hitting multi-month highs, on supply tightness that traders said may have been overestimated. SOF/L]
"I am struggling to find the fundamental justification for the levels we see at the moment," said Jonathan Parkman, head of Fortis Commodity Derivatives' agri-commodity brokerage which watches over cocoa.
In oil, U.S. crude settled down $1.77 at $44.51 a barrel, off a session high of $50.05. London Brent crude closed down $1.81 at $44.60 a barrel.
Economic turmoil has slammed growth in energy demand and contributed to a slide of more than $100 per barrel in oil prices since a July peak of over $147. U.S. crude touched a four-year low of $40.50 a barrel earlier this month.
Prices recovered somewhat over the last week due to threats by producer group OPEC to carry out its largest ever output cut when it meets on Wednesday to address rising inventories and sagging demand.
Among industrial metals, copper for delivery in three months on the London Metal Exchange settled down $5 at $3,170 per tonne.
U.S. copper futures for March finished down 2.35 cents at $1.4050 a lb on the COMEX metals division of the New York Mercantile Exchange.
COMEX gold for February soared $16 to close at $836.50 an ounce.
On the agricultural side, March corn on the Chicago Board of Trade closed up 1-3/4 cents at $3.75-1/4 a bushel. CBOT corn has perked up since last week after influential crop forecaster Informa Economics estimated the 2009 U.S. corn acreage at 82.288 million, down sharply from the 85.9 million tonnes planted in 2008.
CBOT wheat for March closed up 7 cents at $5.20 a bushel, a 1.4 percent gain. (Editing by Marguerita Choy)