GRAINS-Wheat down 1 pct on weak export demand; corn, soy also sag

* Wheat pressured by stronger U.S. dollar

* Corn dragged down by wheat, improved U.S. harvest weather

* Soybeans modestly lower in choppy trade

(Recasts throughout; updates prices, adds quotes; changes byline, dateline, previous PARIS/SYDNEY) CHICAGO, Oct 18 (Reuters) - U.S. wheat futures fell for a third straight day on Wednesday, pressured by plentiful global supplies and strong competition for export business, especially from Russia, traders said. Corn fell, following wheat, while soybeans were modestly lower in choppy trade. As of 12:54 p.m. CDT (1754 GMT), Chicago Board of Trade December wheat was down 4-3/4 cents at $4.30 per bushel after dipping to $4.29, its lowest in nearly a week. CBOT December corn was down 1-3/4 cents at $3.48-1/4 a bushel while November soybeans were down 1/2 cent at $9.84-1/4 a bushel. Wheat slipped more than 1 percent, with the December contract headed for its seventh lower close in the last eight sessions. Strength in the dollar added pressure, making U.S. grains less attractive to those holding other currencies. The U.S. dollar index extended its winning streak to five sessions, supported by rising U.S. Treasury yields. "The slow export pace in wheat and the higher greenback is weighing on prices," said Terry Reilly, senior commodity analyst with Futures International. Reflecting the loss of market share for U.S wheat in Egypt, the world's top importer, U.S. Wheat Associates, a trade group that promotes U.S. exports, is closing its office in Cairo after about 40 years, a spokesman said on Tuesday. Egypt has been sourcing most of its wheat from Russia, which was projected by the U.S. Department of Agriculture to harvest a record-large crop this year of 82 million tonnes. The decline in CBOT wheat futures dragged on corn, along with favorable harvest weather in the U.S. Midwest this week. CBOT December corn was hovering a few cents above its contract low of $3.42-1/2, set last week. Soybeans were choppy, trying to consolidate after a two-session retreat. The benchmark November contract topped $10 a bushel last week for the first time since July, but has backed down this week, due in part to hedge-related selling. "The soybean market confirmed its incapacity to stay above $10 per bushel. The return of dry weather in the U.S. will allow farmers to speed up harvest works," consultancy Agritel said in a note. Brazilian soy producers had planted 12 percent of their 2017/2018 crop through last Thursday, in line with a five-year average but behind the pace of the prior cycle, amid a lack of rain in key producing regions, consultancy AgRural said on Monday.

CBOT prices as of 12:52 p.m. CDT (1752 GMT):

Last Net Pct Volume

change change

CBOT wheat WZ7 429.75 -5.00 -1.2 39305 CBOT corn CZ7 348.00 -2.00 -0.6 99644 CBOT soybeans SX7 984.50 -0.25 0.0 80442 CBOT soymeal SMZ7 322.00 0.40 0.1 27052 CBOT soyoil BOZ7 33.39 -0.20 -0.6 26995

NOTE: CBOT December wheat, December corn and November soybeans shown in cents per bushel, December soymeal in dollars per short ton and December soyoil in cents per lb.

(Additional reporting by Colin Packham in Sydney and Gus Trompiz in Paris; Editing by Marguerita Choy)