GRAINS-Wheat headed for worst week in 2 yrs, but supply woes may boost prices

* Global wheat supply at risk amid hot weather

* Chicago corn futures eye biggest weekly fall in over a year (Adds analyst quotes, updates prices)

MANILA, Aug 24 (Reuters) - U.S. wheat futures dropped for the fifth session in a row on Friday and were on track for their steepest weekly fall in two years as U.S. export sales slowed, although expectations of global supply risks may lift prices in the near term.

Corn prices were headed for their biggest weekly drop in more than a year as results from an ongoing Midwest crop tour fueled expectations of big U.S. harvests.

Chicago Board of Trade wheat for December delivery was down 0.5 percent at $5.39 a bushel by 0227 GMT and had fallen 7 percent for the week, marking the biggest decline since August 2016.

The U.S. Department of Agriculture reported export sales of U.S. wheat in the week to Aug. 16 at 239,800 tonnes, a six-week low, and also below a range of trade expectations for 450,000 to 850,000 tonnes.

Wheat's pullback came after a rally to a three-year high earlier this month on worries that hot weather in many wheat-producing countries could put global production at risk.

"I do think that most of the pressure for wheat is still on the upside," said Phin Ziebell, agribusiness economist at National Australia Bank.

"The reality is there are more emerging supply concerns and the question will be to what extent are they going to be realized. The supply concerns are sufficiently crystallized, particularly in Europe."

Although global wheat stocks are expected to hit an all-time high of 273 million tonnes at the start of the 2018/19 grain marketing season, according to U.S. Department of Agriculture estimates, the problem is nearly half of that is in China, which is not likely to release any into global markets.

Chicago December corn was flat at $3.61 per bushel, but the contract has fallen nearly 5 percent this week, its steepest decline since June 2017.

The Pro Farmer Midwest Crop Tour on Thursday projected above-average corn yields in top growing U.S. state Iowa as well as in Illinois, Indiana, Ohio, Nebraska and South Dakota.

Pro Farmer will release U.S. corn and soybean production estimates on Friday, drawing from tour data.

The International Grains Council raised its forecast for world corn production in the 2018/19 season by 12 million tonnes to 1.064 billion tonnes, largely driven by an improved crop outlook in the United States.

Meanwhile, Chicago soybeans rose 0.2 percent to $8.55-1/2 per bushel on Friday, but have so far fallen 4.2 percent this week. (Reporting by Manolo Serapio Jr.; Editing by Vyas Mohan and Sai Sachin Ravikumar)