CHICAGO (AP) _ Two traders pleaded guilty in plea bargains Thursday and a third pleaded innocent to charges stemming from an undercover FBI investigation of fraudulent trading at the world's largest commodities markets.

William Walsh, 23, and Mark Fuhrman, 39, traders in the Swiss franc pit at the Chicago Mercantile Exchange, each pleaded guilty to one count of wire fraud and one count of making pre-arranged trades in violation of the federal Commodities Exchange Act.

At least five of those indicted, including Walsh and Fuhrman, have agreed to plead guilty and cooperate with prosecutors.

A third indicted trader, Robert Mosky, 33, pleaded innocent to charges of racketeering conspiracy, 26 counts of mail and wire fraud and 37 counts of violating the exchange act.

A federal grand jury indicted 46 people Aug. 2 for trading activities at the Merc or the Chicago Board of Trade. Most charges allege schemes in which traders pocketed profits from trades made for customers while passing their own losses on to customers.

Twelve traders from the Japanese yen pit at the Merc have pleaded innocent.

Walsh and Fuhrman admitted that their actions were part of a pattern of illegal transactions at the Merc. Both implicated Mosky and agreed to testify against him.

Both described transactions with a trader who later turned out to be an undercover FBI agent.

''On October 13, 1988, I entered in a pre-arranged trade with (undercover FBI agent) Randy Jackson ... designed to limit my tax liability and at the same time receive cash back at a later date,'' a downcast Walsh told the judge.

Walsh and Fuhrman face prison terms of up to six years and fines of up to $350,000. They also could face disciplinary action from the Internal Revenue Service and the Commodities Futures Trading Commission.

Both were released on $4,500 personal recognizance bonds.

Mosky also was released under those terms, but agreed that if he sells his seat on the exchange, he must keep the proceeds in escrow pending the outcome of the trial.