CHICAGO, June 27 (Reuters) -

U.S. new-crop corn and soybean futures fell to their lowest in more than a week on Tuesday, pressured by forecasts for much-needed rains in the Midwest where crops have been deteriorating under dry conditions, analysts said.

Wheat futures also tumbled as worries subsided about instability in Russia, the world's top wheat exporter, and the Northern Hemisphere winter wheat harvest progressed.

As of 1:02 p.m. CDT (1802 GMT), Chicago Board of Trade December corn was down 24-1/4 cents at $5.64 per bushel after dipping to $5.55, its lowest since June 15.

CBOT November soybeans were down 25 cents at $12.98 a bushel and September wheat fell 37-1/4 cents to $7.01 a bushel.

Forecasts for rain in the Corn Belt later this week and next week tempered concerns about dry weather that has stressed crops this month.

"Probably the best rain event is coming at us since April. The real question mark for the trade is, do we have a weather pattern change going on, or is this an interlude? We are still going to need regular rains," said Don Roose, president of Iowa-based U.S. Commodities.

The condition of U.S. corn and soybean crops has deteriorated to the worst in decades, U.S. Department of Agriculture data showed on Monday. The USDA rated 50% of the U.S. corn crop and 51% of the soybean crop as good to excellent, down from 55% and 54%, respectively, last week. The ratings were the lowest for this time of year since 1988, a year of historic drought.

As weather outlooks lifted optimism about supplies, questions about demand for U.S. grains lingered, given stiff global competition for export business.

"Brazil's harvest is going to be coming at us, beating us to the punch," Roose said.

Similarly, in the wheat market, the focus turned back towards competitive prices in Russia after jitters caused by the weekend mutiny by the Wagner militia fuelled an early rally on Monday.

The European Union's crop monitoring service MARS on Monday forecast Russia's wheat production this year at 86.7 million metric tons, underlining expectations for an above-average crop.

"Russia has the cheapest (wheat) in the world. They continue to sell it below the world market," Roose said. (Reporting by Julie Ingwersen; additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; editing by Rashmi Aich, Nivedita Bhattacharjee, David Evans and Richard Chang)