Pan American World Airways today formally withdrew from the International Air Transport Association, the organization of 109 world airlines that has traditionally met to set international airline fares and cargo rates.

The announcement of Pan Am's pull-out from the cartel came as several hundred representatives of the international aviation community, in cluding IATA, gathered here for a three-day seminar to discuss the recently changed international aviation policy of the United States and its effects on the rest of the world.

The pro-competition policy America has been pursuing has caused the Civil Aeronautics Board to begin a reexamination of the antiturst immunity it has traditionally granted IATA activities so that U.S. airlines could participate in IATA's rate setting conferences. IATA itself has proposed a reorganization that, if approved by the CAB, would separate the rate making function from the trade association function, thus allowing an airline to participate in baggage, ticketing and other airline functions without getting involved in the fare setting.

Dan Colussy, Pan Am president, said here that Pan Am would participate in IATA trade association activities if the proposed reorganization is approved and implemented. However, he said Pan Am decided to drop out now, effective March 31, without waiting for the reorganization "to make it very clear that Pan Am is not interested in participating in rate and fare conferences at all and is adopting a policy consistent with the U.S. government's.

"We will conduct ourselves in the rate area like any other industry," Colussy said.

Pan Am notified IATA of its decision, which will save the carrier about $1 million a year, in a telegram to Knut Hammarskjold, director general of IATA, who is a participant in the conference here

Hammarskjold said Pan Am's decision wouldn't effect IATA operations very much but "cleared the air of an ambiguity hanging around" while the airline made up its mind what to do. He said he expected Pan Am to be out of IATA "on a temporary basis only" until the reorganization is approved.

Ronald Farmer, director of the CAB's bureau of international aviation, said he didn't think the decision would affect Pan Am's operation but added, "I kind of hope it will affect their prices."

The three-day sumposium on U.S. international aviation policy being held here under the auspices of U.S. State Department is an attempt to explain plain the U.S. air policy and its perceived benefits to a generally skeptical world-wide community

In attendance here are the representatives of more than two dozen nations and 50 airlines.

In remarks prepared for delivery to the opening session Tuseday evening, Jamaican Prime Minister Michael Manley said he hoped the symposium would take up the implications of unrestrained airline competition on economic developments in lesser developed countries with a national airline.

While open competition can lower fares and boost needed tourism, Manley worried that small national airlines of developing countries could not compete -- and survive -- against the big international airlines.

"The fact is that the national airlines in a developing country is not merely a monument of exaggerated self-respect -- and has been unfairly aided by some -- but it is a genuine expression of sovereignty and independence, essential to the maintenance and development of commercial and economic links with the outside world, especially when these services are withdrawn by the larger carriers," Manley said.