CHICAGO, Oct 30 (Reuters) - Chicago wheat futures fell on Friday for a fifth straight session, retreating from multi-year highs set last week, on fund-driven long liquidation and improving crop prospects in the southern U.S. Plains, analysts said.

Soybean futures firmed on export demand while corn settled narrowly mixed, with the front December contract losing relative to back months as speculators rolled long December positions forward into deferred contracts.

Chicago Board of Trade December soft red wheat futures settled down 5-1/4 cents at $5.98-1/2 per bushel after dipping to $5.95-1/4, the contract's lowest since Oct. 14.

CBOT January soybeans ended up 5-3/4 cents at $10.56-1/4 a bushel and December corn finished flat at $3.98-1/2.

All three commodities posted weekly declines, with wheat falling the most at 5.4%. But all three ended higher for the month of October, with corn rising about 5%.

Wheat sagged on Friday on profit-taking and improving weather in parts of the Northern Hemisphere, including the U.S. Plains and Midwest, where storms this week brought welcome moisture.

"We look for crop conditions to improve about 3 percentage points in winter wheat, led by soft wheat," said Terry Reilly, senior analyst with Futures International in Chicago.

The U.S. Department of Agriculture on Monday rated 41% of the U.S. winter wheat crop as good to excellent, down from 56% a year earlier and below analyst expectations, amid dry conditions in the southern Plains.

Worries about dry conditions hurting wheat prospects in the Plains as well as other key suppliers, including Russia and Argentina, had boosted front-month wheat futures to $6.38-1/4 a bushel last week, the highest price in a continuous chart of front-month CBOT wheat in nearly six years.

Managed funds had built a net long position in CBOT wheat futures of nearly 52,000 contracts by Oct. 20, Commodity Futures Trading Commission data showed, their largest since February, leaving the market vulnerable to bouts of long liquidation.

CBOT soybean futures drew support from export demand for U.S. supplies. The USDA on Friday confirmed private sales of 121,500 tonnes of U.S. soybeans to unknown destinations.

(Additional reporting by Nigel Hunt in London and Naveen Thukral in Singapore; Editing by Marguerita)