* US soy harvest seen as 77% complete
* Farmers sell freshly harvested soybeans
* CBOT wheat rises on improved US export demand
CHICAGO, Oct 23 (Reuters) - Chicago Board of Trade soybean futures fell on Monday as advancing U.S. harvests uncovered strong yields and farmers increased sales of their crops, analysts said.
Corn futures also weakened, with the country's harvest more than halfway complete.
"We continue to hear better-than-expected yields, for soybeans in particular," said Brian Basting, commodity research analyst at Advance Trading.
The most active soybean contract was down 4 cents at $12.98-1/4 a bushel by 12:05 p.m. (1705 GMT), after pulling back from a one-month peak on Friday. Corn, which on Friday rose to a 2-1/2 month top before closing lower, was off 2 cents at $4.93-1/2 a bushel.
Farmers are tending to sell more of their freshly harvested soybeans than corn because of solid yields and prices, adding extra pressure on soybean futures, dealers said.
A weekly U.S. Department of Agriculture report due at 3 p.m. CDT (2000 GMT) is expected to show the soybean harvest as 77% complete and the corn harvest as 59% complete, according to a Reuters poll. A week ago, 62% of the nation's soybeans and 45% of the corn crop were harvested.
"U.S. harvest is rolling along with no major issues," Peak Trading Research said in a note.
In Brazil, if expected rains come this week, will improve prospects for soy farmers who have been sowing their new crop at a slower pace in unusually hot and dry weather, experts said.
Heavy rains drenched drought-hit agricultural regions in Argentina over the weekend, which could benefit wheat crops ahead of harvesting and also boost corn planting.
However, CBOT wheat traded 8 cents higher at $5.94 a bushel on improved U.S. export demand. Last month, the market hit a three-year low.
"You've got to get really low to stimulate demand and we've finally seen some of that in the form of Chinese buying," Basting said. (Reporting by Tom Polansek in Chicago. Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Subhranshu Sahu, Eileen Soreng, Jan Harvey and Richard Chang)
