GRAINS-U.S. wheat, corn futures fall; soybeans firm

(Adds closing prices, details)

CHICAGO, July 6 (Reuters) - U.S. wheat futures fell on Thursday, shrugging off signs of further deterioration in already stressed crops, on a round of profit-taking following a rally to multi-year highs, traders said.

Corn futures also fell, snapping a streak of seven straight higher closes, on pressure from the U.S. Agriculture Department's surprise boost to its crop ratings. Soybeans edged higher after an early dip into negative territory spurred technical buying.

MGEX spring wheat posted the biggest decline, shedding 6.2 percent after the front-month contract hit a four-year high earlier this month. MGEX wheat had risen for eight straight sessions.

"The weather up north in the Plains is still hot and dry," said Mark Gold, managing partner at Top Third Ag Marketing. "(But) I think we have extended it a little too far too fast. Everybody and their mother wanted in on the wheat."

K.C. hard red winter wheat and Chicago Board of Trade soft red winter wheat were setting back from two-year highs.

CBOT September soft red winter wheat futures ended down 21 cents at $5.39 a bushel. K.C. hard red winter wheat for September delivery was 23 cents lower at $5.46-1/2 a bushel and MGEX September spring wheat was down 50-3/4 cents at $7.69 a bushel.

USDA said on Wednesday afternoon that good to excellent ratings for U.S. spring wheat dropped 3 percentage points to 37 percent in the latest week. Good-to-excellent ratings for winter wheat fell 1 percentage point.

CBOT December corn futures were 1-1/4 cents lower at $4.02-3/4 a bushel.

The USDA crop progress report showed a 1 percentage point rise in good/excellent ratings for corn to 68 percent, outperforming an average trade estimate of 66 percent.

Private analytics firm Informa Economics on Thursday projected U.S. 2017 corn production at 14.166 billion bushels based on an average yield of 169.7 bushels per acre, trade sources said. That compares with USDA forecasts of 14.065 billion bushels and 170.7 bushels per acre.

CBOT November soybean futures were up 5 cents per bushel at $9.99-1/4. (Additional reporting by Colin Packham in Sydney and Gus Trompiz in Paris; Editing by Dan Grebler and Steve Orlofsky)