Pan American World Airways pilots agreed to give the airline's management concessions valued at $55 million, after having refused for months to consider any wage or benefit reductions. In return, if their proposal is accepted, they will get an undisclosed amount of stock and will sign a four-year contract. The pilots agreed to wage concessions totaling $30 million. The rest would be in work rules changes. The board of Pan Am Corp., the airline's parent, received the proposal at its regular December meeting and delayed action on it until today. The offer came as Pan Am is considering Braniff Inc.'s offer to take over the ailing airline.