Breathing a little heavily in the Andean air, and still dazed at the urgency with which he had been whisked southward (via jet bomber), Dr. Luis Craig walked across packed earth toward a powerful-looking helicopter which, he had just been told, was to take him on the last leg of his trip. He listened tiredly to the unctuous words of his escort, a Lieutenant Rabar who wore the uniform of this Latin American nation's Air Force and who was to fly the helicopter. Shouts erupted behind them, at the e