GRAINS-Corn, soybeans slide on profit-taking, technical selling

* Corn down 1.8 percent on dull demand, rising stocks

* Soy off on technical selling, improved S.America weather

* Firm U.S. dollar adds pressure in grains

(Adds details, updates prices) CHICAGO, Dec 7 (Reuters) - U.S. corn futures fell to a 2-1/2 week low on Friday in the steepest slide in nearly a month, pressured by technical selling and concerns that stockpiles are growing as elevated prices blunt demand. Soybeans retreated from one-month peaks and posted their biggest drop in three weeks in a technical selling and profit-taking setback following four days of gains. Wheat followed corn and soybeans lower. A firm dollar, which increases costs for those holding other currencies, further weighed on grains. "Technically, we pushed up to some tough resistance. When we were at the bottom of the recent trading range, our corn exports and our demand grew. But when we got to the top of the range, they dwindled," said Don Roose, president of U.S. Commodities. "The dollar continues to move higher and the ethanol margins are deep in the red. Weather in the feeding areas is non-threatening, so (livestock) efficiency is up," he said. Chicago Board of Trade March corn fell 13-1/2 cents, or 1.8 percent, to $7.38 a bushel by 1:08 a.m. CST (1908 GMT), on pace for the steepest weekly drop in six weeks. Selling accelerated as the contract broke below its 50-day moving average around $7.48. CBOT January soybeans dropped 13-1/4 cents, or 0.9 percent, to $14.78 a bushel. But the contract remained in position to climb for a third straight week and record the strongest weekly jump in more than three months. January soy briefly rose above its 50-day moving average of $14.96 but failed to hold the gains due to a lack of follow through buying. Traders were also eyeing the contract's looming "death cross," a bearish technical indicator referring to the 50-day moving average breaking below the 200-day moving average. Losses in the front-month soybean contract were deepened by scheduled rolling of long positions by index funds to the next contract month. The "Goldman Roll" is expected to continue for four more days. CBOT March wheat eased 4-1/4 cents, or 0.5 percent, to $8.57-3/4 a bushel and was set for its first weekly decline in three weeks. A monthly U.S. Department of Agriculture report next week is expected to show U.S. corn stocks grew 2.5 percent due to poor export demand, a Reuters poll showed, although stocks will remain the smallest in 17 years due to a crop-crippling drought this year. Soybean stocks are seen tightening to the lowest level since the 2003/04 marketing year (Sept/Aug) amid a scorching export pace, especially to top buyer China, analysts said. USDA on Friday confirmed private sales of 115,000 tonnes of U.S. soybeans to China for 2012/13 delivery. Improved weather in South America, where farmers are expected to harvest the biggest soy crop ever next year, added pressure in soybeans. Rains are expected in Brazil's southern grain-producing states, forecaster Somar said on Friday, a day after the government held its forecast for a record soybean crop despite some concern over dryness.

Prices at 1:11 p.m. CST (1911 GMT)

LAST NET PCT YTD CHG CHG CHG CBOT corn 734.50 -13.25 -1.8% 13.6% CBOT soy 1478.00 -13.25 -0.9% 23.3% CBOT meal 452.10 -5.90 -1.3% 46.1% CBOT soyoil 50.68 -0.19 -0.4% -2.7% CBOT wheat 839.25 -6.00 -0.7% 28.6% CBOT rice 1526.50 -4.50 -0.3% 4.5% EU wheat 268.50 0.75 0.3% 32.6%US crude 86.05 -0.21 -0.2% -12.9% Dow Jones 13,118 44 0.3% 7.4% Gold 1702.57 3.95 0.2% 8.9% Euro/dollar 1.2926 -0.0041 -0.3% -0.1% Dollar Index 80.4090 0.1510 0.2% 0.3% Baltic Freight 966 -24 -2.4% -44.4%

(Additional reporting by Colin Packham in Sydney, Ivana Sekularac in Amsterdam; editing by John Wallace and Marguerita Choy)