(Rewrites throughout with U.S. market activity, adds quotes, updates prices, changes dateline from PARIS/SYDNEY, changes byline)
CHICAGO, Oct 30 (Reuters) - U.S. soybean futures turned lower on Monday on forecasts for crop-boosting rains in some areas of Brazil and as technical selling and month-end positioning weighed on the market.
Corn was narrowly mixed and wheat futures fell for a fourth straight session, with prices for both grains anchored by plentiful global supplies.
Soybeans retreated after posting early gains on easing concerns about dry weather in South America, where farmers are currently planting their next soy crop.
"Showers favored most of the growing areas in Brazil over the weekend, with the heaviest amounts favoring Minas Gerais, Sao Paulo, Parana, and Santa Catarina," said MDA Weather Services meteorologist Kyle Tapley.
The rains, which are expected to continue over the next 10 days, are likely to boost soybean and first-crop corn germination and growth, he said in a note to clients.
Brazilian farmers have sown 30 percent of the soy area through Thursday, roughly in line with a five-year average, but more than 10 percentage points below planting at the same time in the previous year's crop, consultancy AgRural said on Friday.
Reports of large U.S. soybean yields and concerns about lower-than-normal soy protein levels, which could dent export demand, weighed on prices, traders said.
"If you've got a low protein crop, that can take away some of your export demand and shift some of that to higher-protein crops in Brazil," said Terry Linn, analyst with Linn & Associates.
The soybean harvest is expected to be 83 percent complete as of Sunday, along with 53 percent of the corn harvest, according to analysts polled by Reuters. The U.S. winter wheat crop is expected to be 85 percent planted as of Sunday.
Chicago Board of Trade November soybeans, which enter their delivery period on Wednesday, were a penny lower at $9.74-1/4 per bushel as of 12:28 p.m. CDT (1728 GMT), holding below technical resistance at the 20-day and 200-day moving averages of around $9.75. January futures shed 1/2 cent to $9.86 a bushel.
Traders liquidated long positions in soybeans or rolled those positions into deferred contracts ahead of the November futures delivery period.
December corn was 1/4 cent higher at $3.49 a bushel. CBOT December wheat fell 2-1/4 cents to $4.25 a bushel after earlier touching a two-month low. (Additional eporting by Colin Packham in Sydney, Sybille de La Hamaide in Paris and Julie Ingwersen in Chicago; Editing by Chizu Nomiyama)