* Ample corn supply back in focus after rally on USDA data
* Wheat rebound stalls, also pressured by large supply
* Soybeans supported by strong demand from end users, crushers
(Updates with U.S. trading, adds analyst comment)
CHICAGO, Jan 14 (Reuters) - U.S. corn futures fell 1.4 percent on Tuesday as traders locked in profit from the rally that followed a surprise government cut to the U.S. harvest estimate.
Wheat futures also fell, pressured by ample global supplies, but soybeans were firm as demand remained strong despite forecasts for a huge South American harvest, traders said.
Corn futures have rallied 5.4 percent in the last two days, prompting a healthy round of farmer sales of crops they have held in storage since last fall. The country movement pushed down cash basis bids at country elevators and processors and added further weight to futures prices on Tuesday.
"Corn has cooled quickly following the bullish USDA surprise and a 20-cent gift," Matt Zeller, director of marketing information at INTL FCStone, said in a note to clients.
At 10:15 a.m. CST (1615 GMT), Chicago Board of Trade corn for March delivery was down 6 cents at $4.28-1/2 a bushel. Declines accelerated on a wave of technical selling when prices dropped through the 50-day moving average but the market was finding support near its 30- and 40-day moving averages.
The U.S. Department of Agriculture (USDA) stirred up the corn market on Friday by unexpectedly cutting its yield estimate for the 2013 U.S. harvest, while also putting ending stocks below the consensus of trade estimates.
But the smaller-than-expected harvest still provided a key boost to supplies that had been running thin since the drought-reduced harvest of 2012.
"The bigger picture of a large year-on-year increase in U.S. corn supplies still remains intact, so it is difficult to get overly excited about corn prices in the medium term," said Luke Mathews, commodities strategist at Commonwealth Bank of Australia.
Strong end-user demand supported soybean futures. The National Oilseed Processors Association's monthly crush report due Wednesday is expected to show that the U.S. soybean crush was 163.9 million bushels in December, up 2.3 percent from November.
CBOT March soybeans were up 2 cents at $12.96-1/4 a bushel. Trade was volatile and prices briefly fell below their 50-day moving average before some bargain buyers pushed prices higher.
Expectations of a huge boost to soybean supplies in the next few months due to what is expected to be a bumper harvest in South America kept the soy gains in check.
A bountiful supply situation stamped out a bargain-buying rebound in wheat futures and pushed prices lower.
CBOT March soft red winter wheat was 1 cent lower at $5.72-1/2 a bushel. Wheat prices, which were trending near 3-1/2-year lows, have risen in just one of the last seven trading sessions.
Strong harvests around the globe have provided rising competition for U.S. wheat on the export market. Ukraine's Agriculture Ministry raised its forecast for 2013/14 grain exports to 33 million tonnes on Tuesday. Argentina on Monday approved 1.5 million tonnes of wheat exports for the current marketing year.
Prices at 10:18 a.m. CST (1618 GMT)
LAST NET PCT YTD
CHG CHG CHG
CBOT corn 428.50 -6.00 -1.4% 1.5% CBOT soy 1328.00 1.25 0.1% 1.2% CBOT meal 445.10 -1.80 -0.4% 1.7% CBOT soyoil 37.56 -0.01 0.0% -3.2% CBOT wheat 572.75 -0.75 -0.1% -5.4% CBOT rice .00 0.00 0.0% -100.0% US crude 92.11 0.31 0.3% -6.4% Dow Jones 16,335 77 0.5% -1.5% Gold 1247.60 -5.46 -0.4% 3.5% Euro/dollar 1.3677 0.0006 0.0% 0.2% Dollar Index 80.5680 0.0550 0.1% 0.7% Baltic Freight 1370 -25 -1.8% -39.8%
In U.S. cents, benchmark contracts, except EU wheat (euros) and soymeal (dollars). CBOT wheat, corn and soybeans per bushel, rice per hundredweight, soymeal per ton and soyoil per lb.
(Additional reporting by Naveen Thukral in Singapore and Gus Trompiz in Paris; editing by Matthew Lewis)