The Internal Revenue Service is investigating the financial arrangements between Roberto Duran and fight promoter Don King of Duran's unsuccessful defense of his welterweight championship against Sugar Ray Leonard.

The Washington Post also learned tonight that Duran's share of the purse to be paid out by the Louisiana State Athletic Commission was $3.5 million, compared to $7 million paid to Leonard. It had been reported Duran was to earn $10 million.

Duran's share of the purse was held up pending an examination of the Panamanian fighter by a commission doctor on Wednesday. The IRS investigation is not the reason for holding up the purse, however.

Otis Guichet, secretary of the Louisiana State Athletic Commission, confirmed the purse figures for Duran and Leonard. He told The Washington Post "I think the government smells a rat, in the way duran's money is being distributed."

Another source said Emil Bruneaux, chairman of the Louisiana Commission, recieved a written request from the IRS asking him specifically for a copy of Duran's contract. Bruneaux confirmed that, insisting that he would provide information on all the fighters on the card of the IRS.

Another source close to the commission said that a $3 million chunk of the purse in addition to the $3.5 million owed to Duran, is to be paid through a corporation in Panama. That also concerns the IRS, the source said.