* Chicago soybeans move back from Tuesday's 5-week top
* Price curbed by China demand doubts, Brazil crop outlook
* Weekly U.S. wheat export sales top expectations (Updates with U.S. trading, previous PARIS/SINGAPORE)
CHICAGO, Dec 19 (Reuters) - U.S. soybean futures edged lower on Thursday, retreating from a five-week high touched earlier this week as traders expected rains to benefit rival suppliers in South America.
Favorable crop weather could boost production in Argentina and Brazil, increasing global supplies and competition for export business with buyers like China. Rains will ease dry conditions in southern Argentina and also bring relief to drier areas of Brazil, according to Commodity Weather Group.
"We're looking ahead for the forecasts for this weekend," said Brian Hoops, president of U.S. broker Midwest Market Solutions. "It's really beneficial for Argentina, the best rains they've had for several weeks."
Forecasters already expect Brazil to harvest a record soybean crop in the coming months.
For more than a year, China, the world's biggest soy importer, has increasingly turned to Brazil rather than the United States for soybeans due to the trade war between Washington and Beijing.
A long-awaited U.S.-China "Phase 1" trade agreement announced on Dec. 13 buoyed grain markets because it included a commitment by Beijing to expand purchases of U.S. farm products.
But traders remain wary about projections from Washington that deals will reach $40 billion to $50 billion within two years, compared with $24 billion before the trade dispute.
"There's expectations that they're going to buy more soybeans, more corn, more DDGs," Hoops said, referring to the livestock feed distillers' dried grains (DDGs). "But when they make those purchases will definitely affect our balance sheets."
The most active soybean contract on the Chicago Board of Trade (CBOT) was down 4 cents at $9.24-1/2 a bushel by 11:30 a.m. CST (1730 GMT). The market on Tuesday climbed to its highest since Nov. 8 at $9.31 before closing marginally lower on Wednesday.
Corn was up 1/2 cent at $3.87-1/2 a bushel, near a six-week high of $3.90-1/2 touched on Tuesday. Wheat was up 1/2 cent at $5.48-3/4 a bushel at the CBOT. The market ended lower on Wednesday, when it retreated from a 5-1/2 month high struck on Tuesday.
The U.S. Department of Agriculture (USDA) said that export sales of wheat totaled 868,600 tonnes last week, topping analyst forecasts that ranged from 200,000 tonnes to 600,000 tonnes.
Corn export sales were 1.709 million tonnes for the 2019/20 season and 536,100 tonnes for 2020/21, the USDA said, within trade expectations. (Reporting by Tom Polansek in Chicago; Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Rashmi Aich, Alexandra Hudson and Sonya Hepinstall)