(Adds closing prices, analyst comments, details on wheat futures)
* Traders watch for American soy, corn sales to China
* U.S. farmers worry China will more buy Brazil soy
* Beneficial rains boost Brazil harvest prospects
CHICAGO, Dec 26 (Reuters) - U.S. corn, soybean and wheat futures approached one-month lows on Wednesday on worries over export demand and increasing competition for global sales.
Traders were disappointed that there were no signs of additional sales of U.S. soybeans to China, the world's top importer of the oilseed, or of corn.
China bought U.S. soybeans on Dec. 12 in the first big deals in six months, after U.S. President Donald Trump and his Chinese counterpart Xi Jinping met on Dec. 1 and set a 90-day negotiating window to resolve their trade differences.
Soybean futures reached their highest level since midsummer on the day of the sales. They have since dropped about 6 percent as traders said the pace of deals with China was slower than expected.
"A bull needs to be fed every day on some China news, and we didn't have it," said Don Roose, president of Iowa-based broker U.S. Commodities.
Chicago Board of Trade March soybean futures tumbled 1.5 percent to $8.83 a bushel. That most actively traded contract earlier dropped to $8.82-1/2, its lowest price since Nov. 27.
Most-active March corn futures dropped 1.2 percent to $3.73-1/4 a bushel and reached their lowest price since Nov. 29. CBOT March wheat lost 1.2 percent to $5.10 a bushel and touched its lowest price since Nov. 30.
Wheat futures remained under pressure after Russia, the world's top wheat supplier, raised its grain export forecast last week, Roose said.
"The wheat market is still having a hangover," he said.
The U.S. Department of Agriculture is not publishing details of daily export sales during the federal government's partial shutdown.
New USDA data showed the United States inspected 651,181 tonnes of soybeans for export last week, though. That was below analysts' expectations.
"Traders are trading blind here because of the government shutdown," said Mark Gold, founder of Top Third Ag Marketing in Chicago.
"With the big carryouts, there's a move to the path of least resistance, and there is nothing showing that there are big export numbers happening in soybeans, which is what the market really needs to see."
Beijing maintains hefty tariffs on imports of American soy that were imposed as part of the trade war and has looked to South America to replace U.S. cargoes.
American farmers, who have large supplies in storage, worry that trend will continue because Brazil is set to harvest a large crop. Brazil and Argentina recently received rains that should help crops develop, traders said. (Reporting by Tom Polansek in Chicago. Additional reporting by PJ Huffstutter in Chicago; editing by Jonathan Oatis)