ASHINGTON, April 17 — On the third day of the Iraq war, a mysterious American aircraft loitered high over Baghdad for hours on end, evading a withering barrage of missile and artillery fire.Even as Iraqi television showed gunmen shooting into the Tigris River's banks at a phantom plane, the real aircraft — a stripped-down, remotely piloted RQ-1 Predator drone — was landing in a lake 75 miles away, its secret 33-hour mission accomplished: to flush out Baghdad's vaunted air defenses so they could be pinpointed and attacked by waves of allied fighter-bombers.Remotely piloted aircraft like the Predator have played...