(Rewrites throughout, adds quote, updates prices, changes

dateline from PARIS/CANBERRA)

By Karl Plume

CHICAGO, Aug 14 (Reuters) -

U.S. soybean futures declined for the first time in four

sessions in a profit-taking setback on Thursday after a rally

ignited by the U.S. government's lower-than-expected harvest

outlook took prices to six-week highs.

Concerns about soybean export demand due to trade

tensions with top buyer China continued to hang over the market.

Corn futures drifted lower under continued pressure from

the U.S. Department of Agriculture's bigger-than-expected

harvest forecast earlier this week, although strong export

demand limited losses.

Chicago Board of Trade wheat, meanwhile, dropped to

fresh contract lows on ample global supplies.

Grains markets stumbled after this week's soybean-led

advance, and traders are awaiting further production updates

from private forecasters, including from a large corn and

soybean crop tour scheduled to survey yield potential across

seven states next week.

November soybeans were down 14-3/4 cents at

$10.29-1/2 a bushel at 12:30 p.m. CDT (1730 GMT) earlier

climbing to its highest point since July 3.

"We had a 60-cent rally from the lows in soybeans last

week and that's probably about enough," said Jack Scoville,

analyst with the Price Group.

"And even though we're going to have less supplies, I

don't think anybody's of the opinion that the Chinese are going

to be buying anything soon, so we still have to find homes for

all those beans," he said.

U.S. soybean exporters

risk missing out

on billions of dollars worth of sales to China as

trade talks

between Washington and Beijing drag on, according to

traders.

December corn futures were down 1 cent at

$3.96-1/4 a bushel as strong export demand blunted supply

pressure from a likely record-large U.S. crop.

CBOT September wheat was down 4-1/4 cents at

$5.03 a bushel after sliding, along with all other contract

months, to a fresh lifetime low.

(Additional reporting by Gus Trompiz in Paris and Peter Hobson

in Canberra; Editing by Marguerita Choy)