* China manufacturing survey, Fed stimulus exit plan weigh
* CRB index down 2.5 pct, biggest drop since Dec 2011
* Gold at 2-1/2 year low, crude oil sinks 3 pct
* Copper at 20-month low; aluminum, nickel multiyear lows
* Corn, soy and wheat not spared; sugar, coffee tumble

NEW YORK, June 20 (Reuters) - Commodities suffered their biggest selloff in a year and a half on Thursday as bleak Chinese data and the U.S. Federal Reserve's plan to reduce its stimulus efforts hurt the outlook for global growth. Gold hit a 2-1/2 year low and oil sank 3 percent. Copper prices dropped to a 20-month low while aluminum and nickel fell to multiyear lows on worries about slowing factory activity in China, the world's largest buyer of metals. Agricultural markets were not spared either, with corn , wheat and soybeans all down and sugar and coffee setting multiyear lows. A broad rally in the dollar, powered by Fed Chairman Ben Bernanke's outline on Wednesday of a possible timeline for the U.S. central bank's winding down of its stimulus, led to steep declines in commodities denominated in the greenback.

"Today's slide could be one for the history books, at least in gold," said Edward Meir, an analyst at INTL FC Stone. The 19-commodity Thomson Reuters-Jefferies CRB index was down 2.5 percent, its sharpest decline since December 2011. Gold and silver fell to a September 2010 low after Bernanke said the Fed could start paring $85 billion of monthly bond purchases later this year its . The flood of easy money created by the Fed since the 2008-2009 financial crisis has been integral to rallies in gold and other commodities. Bernanke indicated the stimulus programs could stop by mid-2014 if the U.S. economy is strong enough. His remarks went far beyond a communique by Fed policymakers earlier on Wednesday after a two-day meeting, which said the central bank will continue its bond purchases for now and "closely monitor incoming information on economic and financial developments in coming months." "Once the U.S. Federal Reserve starts to taper the asset purchases, we are likely to see a stronger U.S. dollar. Commodities that are priced in the dollar will tend to weaken in this kind of environment," said Lee Chen Hoay, investment analyst at Phillip Futures in Singapore.

Gold's selloff accelerated after it broke through its April low of $1,321 an ounce, a key support level, to touch $1,285 levels. 4 percent at $1,301.56 an ounce by 1440 GMT. U.S. gold futures for August delivery were down more than $74 to hover at $1,298 an ounce. Oil prices fell around $3 a barrel after a survey of Chinese manufacturing activity in June heightened the risk of a sharper slowdown this quarter in the world's second-largest oil consumer. Benchmark Brent crude oil out of Europe's North Sea traded below $103 a barrel versus Wednesday's close of $106.12 In New York, the front-month contract for U.S. crude hovered around $95 a barrel after the previous session's settlement at $98.24. Copper's slide was pressured partly by climbing stockpiles of the metal at warehouses monitored by the London Metal Exchange. Inventories are at around 10-year highs, contributing to the 14 percent drop in prices this year. <MCUSTX-TOTAL> Copper's benchmark three-month futures contract on the LME fell to $6,750 per tonne, its lowest level since Oct. 20, 2011. It was down 2.7 percent at $6,770 by 1438 GMT.

Prices at 10:56 a.m. EDT (1456 GMT)
LAST NET PCT YTD CHG CHG CHG US crude 95.70 -2.54 -2.6% 4.2% Brent crude 103.06 -3.06 -2.9% -7.2% Natural gas 3.888 -0.075 -1.9% 16.0% US gold 1296.60 -77.20 -5.6% -22.6% Gold 1297.11 -53.58 -4.0% -22.5% US Copper 3.06 -0.08 -2.5% -16.1% LME Copper 6791.00 -169.00 -2.4% -14.4% Dollar 82.057 0.629 0.8% 6.9% CRB 280.668 -7.290 -2.5% -4.9% US corn 673.50 -8.75 -1.3% -3.5% US soybeans 1509.25 -13.75 -0.9% 6.4% US wheat 702.25 -4.75 -0.7% -9.7% US Coffee 117.65 -5.10 -4.2% -18.2% US Cocoa 2193.00 -43.00 -1.9% -1.9% US Sugar 16.46 -0.51 -3.0% -15.6% US silver 19.935 -0.017 -7.8% -34.0% US platinum 1376.60 -47.30 -3.3% -10.5% US palladium 677.55 -17.30 -2.5% -3.7%