* Corn poised for biggest weekly gain since late Jan, up 7% * Wheat set for 3rd weekly gain, soybeans up 5.6% this week (Recasts with details wheat market; adds quote in paragraph 3, fund positioning) SINGAPORE, April 23 (Reuters) - Chicago corn slid on Friday as the market paused after climbing to its highest in nearly eight years, although concerns over tightening world supplies kept the grain on track for its biggest weekly rise since late January. Wheat gained more ground and was on course for its biggest weekly climb in almost two years on expectations of strong demand and lower production in top exporter Russia. “The ongoing issues of China’s demand and Brazil’s supply continue to boost the market,” said Tobin Gorey, director of agricultural strategy at Commonwealth Bank of Australia. “Added to that are signs that US ethanol demand (is) recovering.” The most-active corn contract on the Chicago Board of Trade (CBOT) lost 0.9% to $6.25-3/4 a bushel by 232 GMT, having earlier hit a June 2013 high of 6.35 a bushel. For the week, it was up 7%, set for the biggest one-week gain since Jan. 29 and fourth weekly rise. Soybeans were up 5.6% for the week and wheat has added 8.6%, with both set for their biggest weekly rise since May 2019. U.S. corn and soybean harvests are dwindling, and traders remain concerned about a U.S. cold spell this week and dryness in Brazil threatening prospects for the next crop. In the wheat market, lower output and strong demand are supporting prices. Russian agriculture consultancy IKAR has downgraded its forecast for Russia’s 2021 wheat crop to 79.5 million tonnes from 81 million tonnes, it said on Thursday. Chinese buyers are thought to have booked at least half a million tonnes from the next French wheat harvest, as China looks widely to cover grain import needs heightened by a domestic corn deficit, traders said. The sales were believed to be the first confirmed deals involving the 2021 crop and suggest China will remain a major outlet for French wheat for a third consecutive season. Commodity funds were net buyers of Chicago Board of Trade corn, soybean, wheat, soyoil and soymeal futures contracts on Thursday, traders said. (Reporting by Naveen Thukral; Editing by Subhranshu Sahu) In the wheat market, lower output and strong demand are supporting prices. Russian agriculture consultancy IKAR has downgraded its forecast for Russia’s 2021 wheat crop to 79.5 million tonnes from 81 million tonnes, it said on Thursday. Chinese buyers are thought to have booked at least half a million tonnes from the next French wheat harvest, as China looks widely to cover grain import needs heightened by a domestic corn deficit, traders said. The sales were believed to be the first confirmed deals involving the 2021 crop and suggest China will remain a major outlet for French wheat for a third consecutive season. Commodity funds were net buyers of Chicago Board of Trade corn, soybean, wheat, soyoil and soymeal futures contracts on Thursday, traders said. (Reporting by Naveen Thukral; Editing by Subhranshu Sahu)