* Soybeans retreat from highest levels since March 21

* Flooding in Brazil's top-producing state raises concerns

* Wheat falls 1.7%, eases after two sessions of gains

SINGAPORE, May 6 (Reuters) - Soybeans slid on Monday as the market took a breather after climbing to a six-week high earlier in the session, with floods in Brazil's key growing state threatening to reduce supplies from the world's top exporter.

Wheat prices slid 1.7%, giving up some of the recent gains, which were triggered by dry weather in top exporter Russia, while corn fell for the first time in four sessions.

The most-active soybean contract on the Chicago Board of Trade (CBOT) was down 0.6% at $12.08 a bushel, as of 0409 GMT, after climbing to its highest since March 21 at $12.19 a bushel earlier on Monday.

Wheat fell 1.8% to $6.11-1/4 a bushel and corn lost nearly 1% to $4.56 a bushel.

The outlook for the soybean harvest in Rio Grande do Sul, which was on track to become the second-largest producer in Brazil behind Mato Grosso state, is deteriorating swiftly after torrential rains flooded fields, with about a quarter of beans to be reaped.

The state is also Brazil's sixth-largest corn producer.

In Argentina, corn stunt disease spread by leaf-cutter insects and adverse weather prompted the Buenos Aires grains exchange to slash its estimate for Argentina's 2023/24 corn harvest by 3 millions metric tons to 46.5 million tons.

Worries of crop losses in Russia have been driving gains in the wheat market over the past few weeks, with CBOT wheat up 8% in April.

"Speculators have held bearish bets in Chicago wheat for nearly two years, but excessively dry weather in top exporter Russia as well as concerns for other global wheat crops have recently ignited notable short covering," Karen Braun, a market analyst for Reuters, wrote in a column.

Russia's IKAR agricultural consultancy has cut its forecasts for Russia's wheat crop to 91 million tons from 93 million tons and wheat exports to 50.5 million tons from 52 million tons, it said on Friday.

Large speculators trimmed their net short position in Chicago Board of Trade corn futures in the week ended April 30, regulatory data released on Friday showed.

The Commodity Futures Trading Commission's weekly commitments of traders report also showed that non-commercial traders, a category that includes hedge funds, trimmed their net short position in CBOT wheat and trimmed their net short position in soybeans.

(Reporting by Naveen Thukral; Editing by Rashmi Aich and Sherry Jacob-Phillips)