CHICAGO, JAN. 9 -- A federal jury convicted six soybean brokers and four independent traders of racketeering charges today, giving the government its first major victory in a massive investigation of futures trading fraud in Chicago.

All 10 defendants were found guilty of at least one count of the lesser charges of mail or wire fraud in a trial that was closely watched by the futures markets, one of Chicago's most important businesses.

The brokers and traders from the Chicago Board of Trade were charged with a total of more than 300 offenses including racketeering, mail fraud, wire fraud and violations of the federal Commodities Exchange Act. Nine of the defendants were charged with racketeering. Only broker William Barcal III was acquitted of that charge.

The victory buoyed prosecutors who got lesser convictions in the first trial stemming from the 1989 FBI sting investigation at the CBOT and Chicago Mercantile Exchange that led to 48 indictments.

Assistant U.S. Attorney Ira Raphaelson, one of three prosecutors in the case, said of today's verdict, "All 10 defendants were convicted of the fraud theory we were told wouldn't hold water." But George Collins, attorney for broker Bradley Ashman, indicated an appeal was likely.

Prosecutors alleged the 10 were involved in illegal after-hours "curb trading," part of a conspiracy in which brokers illegally passed personal losses from trading errors on to cooperative independent traders in return for guarantees of later profitable trades.

Lawyers for several of the defendants conceded they engaged in curb trades and violated other rules, but they said the actions did not constitute fraud and customers were not hurt.

The jury began deliberating Dec. 10 in the trial, which began Sept 10. It considered charges against soybean brokers Barcal, Ashman, Edward Cox III, Martin Dempsey, Thomas Kenney and John Ryan, and traders Charles Bergstrom, Joel Fetchenhier, Sheldon Schneider and John Vercillo.

All the defendants except Ryan were charged with racketeering or racketeering conspiracy, which carry maximum penalties of 20 years in prison, a $250,000 fine and forfeiture of personal assets. Each count of mail fraud, wire fraud or commodities fraud carries a maximum penalty of five years in prison and a $250,000 fine.

CBOT Chairman William F. O'Connor said in a prepared statement that "while any indictment or conviction is one too many," the number of members indicted in the government investigation was less than 1 percent of the exchange's membership.

"I believe at the CBOT we have the most honest members of any exchange," O'Connor said. "Therefore, we do not tolerate any infraction of our exchange rules."