GRAINS-U.S. corn price gains 1 pct on U.S. weather worries

(Updates prices, adds analyst comments; changes byline, dateline, previously HAMBURG)

* Corn trims earlier gains amid shifting weather models

* Soy, wheat firm, following corn prices higher

* Egypt buys wheat from Russia, Romania and France

CHICAGO, July 18 (Reuters) - Chicago Board of Trade corn

futures climbed about 1 percent on Tuesday, lifted by

concerns hot and dry weather could reduce yields for the U.S. harvest in the wake of government data showing deteriorating crop condition ratings, traders said. Corn trimmed earlier gains at midday and prices remained volatile amid shifting weather models that predicted varying levels of heat and precipitation.

CBOT September corn was up 3-3/4 cents to $3.78-3/4

per bushel at 12:29 p.m. CDT (1729 GMT), off its peak of $3.88-3/4.

CBOT soybean and wheat futures also were

higher, tracking moves in corn and MGEX spring wheat futures . Spring wheat prices were the highest in nearly a week as drought took its toll on fields in the northern Plains. "Weather is most critical for corn and that's the (commodity) leading the way," Zaner Group broker Ted Seifried said. "There's definitely some areas of concern that can have a big impact if we're dealing with stress." The U.S. Department of Agriculture late on Monday said 40 percent of the U.S. corn crop was going through the silking portion of its pollination phase as of Sunday. Hot temperatures and a lack of moisture could limit yield potential for corn plants. USDA also slashed good-to-excellent condition ratings for the corn, soybean and spring wheat crops, a move that analysts anticipated. "The weather outlook for the coming week is pointing toward above-average temperatures for the U.S. corn belt," said Angus Thornton, commodity analyst at Profarmer. "In the next two weeks U.S. corn regions need widespread rains. But forecasts remain for generally hot weather with extensive rain not expected."

CBOT August soybeans were 5-3/4 cents higher at

$9.90-3/4 per bushel.

CBOT September wheat edged up 1-3/4 cents to $5.07-3/4 per bushel and MGEX September spring wheat 10-1/4 cents

higher to $7.77-1/2 per bushel. K.C. September hard red winter

wheat was 3 cents higher $5.09-1/2.

The state grain buyer for top global wheat importer Egypt said it purchased 300,000 tonnes of Russian, Romanian and French wheat. No U.S. wheat was offered in the tender, and overall tepid global demand for U.S. supplies has capped potential price gains despite concerns about U.S. crop conditions, traders said.

(Additional reporting by Michael Hogan in Hamburg and Colin Packham in Sydney; Editing by Marguerita Choy)