* CBOT soy backpedals from Nov. 30 high

* Unknown destinations buy US soybeans -USDA

* Wheat, corn futures trade firmer

CHICAGO, Dec 12 (Reuters) - Chicago Board of Trade soybean futures backpedaled on Tuesday after reaching their highest price in December as traders assessed risks from unfavorable crop weather in Brazil.

Wheat and corn futures advanced.

Traders continue to closely watch Brazilian weather because it is the world's top soybean supplier and competes with the U.S. for export business. Heat and dryness have hurt crops in northern and central areas, though analysts said midday forecasts on Tuesday looked wetter than outlooks earlier in the session.

"Losses are substantial for some farmers, but a short distance away, crops look good," said Arlan Suderman, chief commodities economist for brokerage StoneX.

Reductions in Brazilian harvest estimates are "not big enough cuts yet to demand an increase in U.S. exports," he added.

The U.S. Department of Agriculture, in a daily announcement, confirmed sales of 198,000 metric tons of U.S. soybeans to unknown destinations. It was the fifth consecutive session in which the USDA reported a daily U.S. soy sale to China or unknown destinations.

"This good sales momentum was compounded by fears of a deterioration in yield potential in Brazil, where weather conditions seem unfavorable this week," consultancy Agritel said.

Most-active CBOT soybeans ended down 12-1/4 cents at $13.23-3/4 per bushel after rising earlier to its highest price since Nov. 30. Sharp losses in energy markets also weighed on soybean and soyoil futures, brokers said.

CBOT corn rose 3-3/4 cents to close at $4.85-1/4 per bushel.

Wheat settled up 16 cents at $6.25-1/2 a bushel amid short covering, traders said, after rallying last week on a string of sales of U.S. soft red winter wheat to China.

"Yesterday we didn't make a wheat sale for the first time in a while," said Jim Gerlach, president of brokerage A/C Trading. "Today's action makes me think maybe we have."

In global demand news, traders said

Algeria

and

Tunisia

bought wheat in separate international tenders. (Reporting by Tom Polansek in Chicago. Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Marguerita Choy and Andrea Ricci)