GRAINS-Soy at three-week high on U.S. exports, wet Argentina

* Slow export pace weighs on wheat, corn

* Dry U.S. Plains limit declines in wheat

(Updates prices, adds analyst quote) CHICAGO, Nov 29 (Reuters) - U.S. soybeans rose to a three-week high, before gains were pared on Thursday, bolstered during the planting season in Argentina. Corn and wheat declined as much as 1 percent, pressured by disappointing export sales results and by profit-taking following multi-week highs earlier this week. U.S. export sales of soybeans, corn and wheat were the smallest in three weeks last week, with each missing trader expectations, U.S. Agriculture Department data showed on Thursday. However, only three months into the soybean marketing season, exporters have already sold 75 percent of what the U.S. Agriculture Department estimated for the entire year. "Most of the crop markets reacted negatively to USDA's export sales report this morning," analyst Richard Brock of Milwaukee's Brock and Associates said in a note to clients. Export sales of U.S. soymeal last week were the highest in two months amid tight supplies in South America. Rains are expected in the coming days and likely to delay planting in Argentina, the No. 1 exporter of soymeal and soyoil. "You have an underlying bullish force," said Jason Britt, president of brokerage Central State Commodities in Kansas City. "We are not slowing exports, even though today's numbers were a little lower." Chicago Board of Trade January soybeans were up 1/2 cent to $14.46-3/4 per bushel as of 12:20 p.m. CST (1820 GMT) while the March and May contracts posted larger gains. Those months are when South American farmers will be harvesting their crops. Wet weather is a mounting issue in Argentina while overall satisfactory crop weather continues in Brazil, said Andy Karst, meteorologist for World Weather Inc. "It's still too wet in Argentina and there are a couple more rounds of rain coming over the next week, so there won't be a whole lot more planting going on," he said. "It looks drier after the first week of December in Argentina, which will help, and Brazil looks good with frequent showers so there's not a whole lot of concern in Brazil for now," Karst said.

U.S. PLAINS STAY DRY CBOT March wheat eased 6-3/4 cents to $8.84-1/2 per bushel, a decline of 0.8 percent and the first drop in eight sessions. CBOT March corn shed 4 cents to $7.60 per bushel, its first drop in four sessions. Drought conditions in the U.S. hard red winter wheat belt spurred the longest rally in wheat futures since July before prices eased as traders took profits on Thursday. Still, dry weather in the U.S. Plains continues to cause concern about the newly seeded HRW wheat crop, Karst said. "There is not a whole lot of rain or snow seen for either the Plains or the Midwest for the next week to 10 days. Maybe a light shower or two in the Midwest, but nothing significant," he said.

Prices at 12:20 p.m. CST (1820 GMT)

LAST NET PCT YTD CHG CHG CHG CBOT corn 760.00 -4.00 -0.5% 17.6% CBOT soy 1446.75 0.50 0.0% 20.7% CBOT meal 442.60 2.70 0.6% 43.1% CBOT soyoil 49.94 -0.17 -0.3% -4.1% CBOT wheat 884.50 -6.75 -0.8% 35.5% CBOT rice 1519.00 0.00 0.0% 4.0% EU wheat 273.75 -2.25 -0.8% 35.2%US crude 88.04 1.55 1.8% -10.9% Dow Jones 13,017 31 0.2% 6.5% Gold 1727.50 8.19 0.5% 10.5% Euro/dollar 1.2970 0.0019 0.1% 0.2% Dollar Index 80.2070 -0.1290 -0.2% 0.0% Baltic Freight 1097 -7 -0.6% -36.9%

(Additional reporting by Sam Nelson and Karl Plume in Chicago; Editing by Dale Hudson and Bob Burgdorfer)