In a column on Aug. 8, Jack Anderson and Dale Van Atta rehashed discredited charges made against John Hull, an American who permitted his farm in northern Costa Rica to be used to help supply the Nicaraguan freedom fighters.

These columnists wrote of Mr. Hull, ''When Costa Rica arrested him for drug trafficking, Hull jumped bail and came home. Now he's wanted for murder in Costa Rica.''

John Hull is a fine American, a veteran of World War II who volunteered to help the Nicaraguan freedom fighters in their effort to rid their country of the corrupt, Communist Ortega regime. Because of this, a leftist prosecutor in Costa Rica had him imprisoned without bail on charges of drug-smuggling and committing hostile acts against a neighboring country. Mr. Hull had a heart attack and nearly died in jail. He was finally released on bail, and the drug-smuggling charges were dismissed. Mr. Hull then learned that the prosecutor was planning to charge him with murder, which would enable the prosecutor to jail him indefinitely without bail. Mr. Hull, who came to the United States to undergo heart surgery, decided not to return to Costa Rica.

The murder charge was based on a suit filed in Miami by an extreme leftist group called the Christic Institute. It charged John Hull and 28 others, including retired Maj. Gen. John K. Singlaub and retired Maj. Gen. Richard Secord, with being involved in a vast conspiracy to commit all kinds of crimes, including drug smuggling and murder. A federal judge in Miami dismissed the suit and ordered the plaintiffs to pay more than $1 million dollars to cover the legal costs of the defendants as a penalty for bringing a frivolous suit. Two weeks before Messrs. Anderson and Van Atta smeared Mr. Hull, Costa Rica's leading paper acknowledged that the charges against him were dubious. Mr. Hull is confident that he will be completely cleared in the near future.

REED IRVINE Chairman, Accuracy in Media Washington