It was the third orbit of the Gemini 4 voyage, and into the silent void of space stepped Astronaut Edward White. If all went well -- and indeed it did, gloriously -- White and his command pilot, Major James McDivitt, would make 62 trips around the world. From the moment he began his 17,500-mph space walk, White felt a bubbling euphoria at seeing his world as no fellow Astronaut had ever seen it before. Neither below him nor above him, but simply out there was the planet Earth -- of which he himse lf was now a satellite. Seen from 120 miles away, far from its gritty sidewalks and smogs and billboards and traffic jams, it was a luminous globe, bluer than any sapphire, infinitely remote and mysterious. But for its spectacular aspects, White's space w alk was no mere stunt. It was a deliberate and methodical test of the techniques which future astronauts may have to sue in docking maneuvers and making extraterrestrial emergency repairs. For 12 of the 20 minuets that White floated and maneuvered outside his spacecraft, two rapid-sequence cameras on board the ship recorded his movements. White himself used a camera attached to his propulsion gun, and McDivitt operated another at his window inside. Thus when Gemini 4 had completed its mission and came str eaking back through the atmosphere like a homing meteor, it brought hack the extraordinary pictorial log shown in color on these pages.