* Rains would boost prospects for Argentina soy crop
* EU wheat prices ease as firm euro adds to export challenge (Add quotes, updates prices)
LONDON, Dec 14 (Reuters) - U.S. soybean prices declined on Thursday as forecasts called for much-needed rains in Argentina, while Chicago wheat and corn futures were little changed.
The most-active soybean contract on the Chicago Board of Trade was down 0.5 percent at $9.74 a bushel at 1127 GMT, with the market back on the defensive after a short-covering rally on Wednesday.
"Argentinas dry soybean crops remain an important prop for the market," Commonwealth Bank of Australia analyst Tobin Gorey said in a market update.
"Weather forecasters are becoming less confident the hot and dry conditions will persist. Any suggestion of a rain event for the region might quickly undermine soybean prices."
Rains expected this weekend in Argentina's main soy and corn growing areas will provide some relief to drought-stricken parts of the country's central farm belt, holding out hope that crop losses may yet be minimal, meteorologists said on Tuesday.
CBOT's most-active wheat contract was up a marginal 0.1 percent at $4.17-1/4 a bushel, finding some support after dropping to the lowest in 11 months on Tuesday.
Dealers said, however, supplies remained abundant.
The U.S. Department of Agriculture this week raised its forecast for world wheat stocks in 2017-18 to a new record, while also increasing the expected stockpile in the United States.
The agency lifted its estimate for global wheat inventories at the end of June 2018 to an all-time high of 268.42 million tonnes, up from last year's record stocks of 255.33 million tonnes.
March milling wheat on Paris-based Euronext was down 0.5 percent at 159.75 euros a tonne.
Dealers said a firm euro was weighing on European prices.
"European operators, and especially French, are closely monitoring the exchange rate, crucial for the export activity which is especially challenging this season due to the number of competitors," analysts Agritel said in a market note.
Farm office FranceAgriMer cut its outlook for French 2017/18 soft wheat exports outside the European Union on Wednesday for the second month in a row to take account of intense competition on world markets.
CBOT's most-active corn contract was down a marginal 0.1 percent at $3.48-3/4 a bushel. (Additional reporting by Naveen Thukral; Editing by Dale Hudson)