MIAMI (AP) _ Southern Air Transport advanced money to a secret buyer to purchase the cargo plane that later was shot down on a weapons supply run to Nicaraguan rebels, the company's president said in an interview published Wednesday.

President William G. Langton told The Miami Herald that Southern Air paid Harry Doan, a Daytona Beach airplane trader, more than $300,000 by cashier's check for the C-123 cargo plane six months before it was shot down.

The anonymous customer needed the plane but did not have the cash available at the time, Langton said.

The plane was shot down Oct. 5 while attempting to deliver weapons to Nicaraguan opposition forces. The sole survivor of the crash, Eugene Hasenfus, was imprisoned by the country's government.

Langton said he granted the interview largely because of erroneous news reports and speculation that Southern Air still is linked to the CIA, which owned the company from 1960 to 1973.

''This company has no connection or affiliation with the CIA, period,'' Langton said. ''We are a cargo carrier. We haul cargo for our customers.''

Langton also said Southern Air flew United States arms to Israel for later shipment to Iran. Southern Air flew the arms at the request of the National Security Council, but never carried the weapons beyond Israel, he said.

The company has received subpoenas from Senate and House investigative panels to testify on Southern Air's role in arms shipments, Langton said. The Senate Intelligence Committee demanded all company flight records for the past two years and other data, some of which already has been provided, he said.

''Am I going to cooperate? Absolutely, absolutely,'' Langton said. ''I would respond freely to all questions at any hearing.''

Langton said any further comment on arms shipments would come before the committees.

''Our total involvement will come out in the hearings because I am going to be very straightforward on this,'' he said. ''We have a good deal of knowledge about the entire activity, and that's all I want to say about that.''