The exhibit neither hides nor harps on the Enola Gay's role in helping to end World War II and begin the Atomic Age. The airplane, painstakingly restored, is presented chiefly as an important artifact in the history of aviation and air power. The protesters are angry because the Enola Gay is being displayed the way everything else in the National Air and Space Museum is displayed: simply. This past Sunday three more protesters hurled ashes and what they claimed was human blood on the fuselage of the aircraft. Three weeks earlier, vandals had splattered the gallery with red paint. As hundreds of visitors waited in line to see the B-29 that delivered the first atomic bomb over Hiroshima, a handful of demonstrators waving anti-nuclear placards kneeled at the entrance to the exhibit, shouting slogans and singing songs, refusing to move until the police finally hauled them off. WASHINGTON - The Smithsonian Institution's exhibit on the Enola Gay opened to the public last week, and within hours protesters were doing their best to shut it down.