GRAINS-U.S. soybeans at 3-month low; wheat, corn extend gains

(Updates prices, adds analyst comments; changes byline, dateline, previous LONDON)

CHICAGO, Dec 21 (Reuters) - U.S. soybean futures fell

to a three-month low on Thursday, on pace for the sixth straight session of declines, on pressure from easing vegetable oil prices and improving crop weather in South America.

Wheat and corn futures both were the highest

in more than a week, with prices notching narrow gains on better-than-expected U.S. export sales. Trading volume in grains remained light ahead of Friday's abbreviated session and closure for Monday's Christmas holiday.

Chicago Board of Trade January soybean futures were

down 6 cents to $9.48 per bushel at 12:10 p.m. CST (1810 GMT).

Malaysian palm oil fell 1.7 percent and CBOT soyoil 0.8 percent on outlooks for increased Asian palm

production while recent rains in Brazil and Argentina should aid emerging soy crops there. "Soybeans are methodically building a short position," said Ken Morrison, analyst and author of Morrison on the Markets. More stringent specifications for U.S. soybean imports in China, the top global buyer, added to the bearish headwinds for soybeans. U.S. shipments to China as of Jan. 1 will be required to have reduced foreign material content to expedite unloadings, the U.S. Department of Agriculture said on Wednesday. USDA on Thursday said weekly U.S. export sales of 796,300 tonnes of wheat and 1.6 million tonnes of corn were higher than analyst expectations while sales of 1.7 million tonnes of soybeans were at the high end of estimates. Weekly sales of 191,500 tonnes of soft red winter wheat - the variety traded on the CBOT - were the largest in more than three years. Traders said buyers in Asia took advantage of a recent drop in prices to purchase feed-grade SRW wheat.

CBOT March wheat futures rose to the highest since

Dec. 6, gaining 2-3/4 cents to $4.26-1/4 per bushel. CBOT March

corn futures were up 1-1/2 cents to $3.50-3/4, the highest

since Dec. 12. Both contracts had dipped to lifetime lows earlier this month. "Certainly, at these prices there is some support," said Phin Ziebell, agribusiness economist at National Australia Bank. "But it is a tough bet to see a sustained pick-up in prices as there are ample supplies."

(Additional reporting by Nigel Hunt in London and Naveen Thukral in Singapore; Editing by James Dalgleish)