GRAINS-Soy posts biggest advance this month on Argentine woes

* Soybeans up 1.5 pct on poor rains in Argentina

* Wheat rises on strong demand for U.S. supply

* Market eyes Chinese buying after Lunar New Year break

(Updates prices, adds analyst quotes, details of China's soybean purchase; changes dateline from HAMBURG/SINGAPORE) CHICAGO, Feb 19 (Reuters) - U.S. soybeans rose 1.5 percent on Tuesday, notching the biggest advance this month, on concerns about crop prospects in Argentina amid disappointing rainfall and on renewed Chinese buying. Soybeans also gained support from technical buying on follow-through from an upturn late last week after the market had hit a one-month low on commodity fund long-liquidation. "We saw a shift in momentum late last week so it's technical and also the rains in Argentina, particularly in the south, were disappointing," said Sterling Smith, futures specialist for Citigroup. Spot March soybeans fell to a one-month low on Thursday then reversed course and closed near the session high on Friday. When trading resumed this week, the bellwether contract broke above resistance at its 50-day moving average of $14.38. Next key resistance is at the 100-day and 200-day moving averages of $14.56 and $14.57 respectively. "China bought some old-crop beans and seeing them come back in, I think, was supportive as well," Smith said. The U.S. Department of Agriculture on Tuesday said exporters had sold 120,000 tonnes of U.S. soybeans to China for delivery during the current old-crop (2012/13) marketing year.

Corn and wheat held firm largely due to spillover buying from the jump in soy, with gains restrained by improved crop weather prospects in the United States. Wheat futures also rose because of hopes of strong demand for U.S. supplies, while corn was supported by concern about dryness in Argentina plus possible slower exports from Brazil. "Soybeans are the main price driver today with support coming from concern about the lack of rain in Argentina, which could reduce yield potential for the upcoming Argentine soybean crop," Rabobank analyst Erin FitzPatrick said. "There has been some rain in Argentina but it is still not enough and more wet weather is needed. "Wheat is seeing continued support from good U.S. export figures last week and from good prospects for more export sales as U.S. wheat is just about the cheapest in global markets." At 8:52 a.m. CST (1452 GMT), Chicago Board of Trade March soybeans were up 23-3/4 cents per bushel at $14.48-1/4, March corn was up 2-1/2 at $7.01-1/4 and March wheat was up 3-1/2 at $7.45-3/4. Chicago March soymeal jumped 2.08 percent to $417.90 a ton. "Soymeal is also very firm today as Argentina is the world's largest soymeal exporter and any reduction in the expected soybean crop would have an impact on soymeal export availability," FitzPatrick said. The rain that had been expected to bring relief to wilting Argentine soybean and corn crops over the weekend was lighter than expected, raising the prospect of lower yields in the 2012/13 harvest set to start in coming weeks. Importers are urgently hoping Brazil and Argentina will replenish tight global supplies with their large new crops in early 2013 following a devastating drought in the United States last year. Prices at 8:57 a.m. CST (1457 GMT)

LAST NET PCT YTD CHG CHG CHG CBOT corn 701.25 2.50 0.4% 8.5% CBOT soy 1448.00 23.50 1.7% 20.8% CBOT meal 417.70 8.30 2.0% 35.0% CBOT soyoil 52.07 0.45 0.9% 0.0% CBOT wheat 745.50 3.25 0.4% 14.2% CBOT rice 1571.00 -12.50 -0.8% 7.6% EU wheat 248.25 2.50 1.0% 22.6%US crude 95.85 -0.01 0.0% -3.0% Dow Jones 14,037 55 0.4% 14.9% Gold 1608.14 -1.41 -0.1% 2.8% Euro/dollar 1.3366 0.0015 0.1% 3.3% Dollar Index 80.5410 -0.0390 -0.1% 0.5% Baltic Freight 738 -9 -1.2% -57.5%

(Additional reporting by Michael Hogan in Hamburg and Naveen Thukral in Singapore; Editing by Dale Hudson)