U.S. wheat fell 3 percent to a one-week low and corn fell 2 percent on Wednesday as each posted their biggest daily loss in two months due to long-liquidation by commodity funds ahead of a key U.S. government crop report on Friday, traders said.

Funds sold 24,000 corn contracts the biggest one-day sale by funds in 3-1/2 months, according to trade sources.

Ample world wheat supplies put pressure on Chicago wheat and chart-based selling accelerated selling that pushed the benchmark May contract below chart support at its 50- and 100-day moving averages, both near $6.53 a bushel.

Soybeans, underpinned by damage to South American crops, touched a five-month high in early trading but spillover selling from the tumbling wheat and corn moved soy into the red by Wednesday's close.

"Looking at the gains we've had in the last couple of weeks, traders are reluctant to push above resistance," said Arlan Suderman, market analyst at Farm Futures magazine. "Traders are saying, 'Let's consolidate ahead of Friday's report and then see where USDA is at.' "

Equity markets and crude oil were stronger even as investors awaited the outcome of the Greek debt restructuring deal and fretted about a weaker outlook for the global economy. Chicago Board of Trade May wheat fell 18-1/2 cents at $6.39-1/4. Wheat fell over 2 percent in the previous session on concerns about the global economy.

Some analysts believe the USDA will trim its estimate of 2011/12 U.S. and world wheat stocks in its Friday report to 212.6 million tonnes, from its February forecast of 213.1 million tonnes; however world wheat supplies still look plentiful. Others are not so sure the report will be bullish, especially in its 2012/13 U.S. corn and wheat ending stocks, said Jason Roose, commodity analyst and vice president of Iowa-based U.S. Commodities.

"They're afraid of the crop report coming out. For the last few months, we really haven't had a lot of (production) problems in the world grain market, besides South America." China's cut in its forecasted growth rate on Monday has also raised lingering concerns about the economic outlook in the world's biggest soybean buyer, Roose said.

Chicago May corn dipped 15-1/4 13 cents, to $6.38-3/4 per bushel as sellers followed through from a 1 percent fall on Tuesday. On Monday, May corn nearly reached a two-month high. China's northeast province of Heilongjiang, the country's top corn and soy grower, aims to raise total grains output by 8 percent in 2012 and expand its corn acreage by paring back on land for soy, a local agriculture official said.

Chicago Board of Trade May soybeans slipped 8-1/2 cents to $13.26-3/4 per bushel. The market expects USDA to lift its forecast for U.S. soybean export demand as smaller South American crops transfer demand to the United States. Traders and analysts also predict a reduction in drought-hit Brazil's soybean output. Hamburg-based oilseeds analyst Oil World cut its forecast of Brazil's 2012 soybean crop by 1.5 million tonnes to 68 million tonnes, a day after two industry groups cut their own forecasts.