A 23- year-old Italian protester was shot and killed today by a police officer during a riot less than two miles from a gathering of leaders of the world's largest industrialized nations, who were protected by a 13-foot fence that anti-globalization demonstrators had vowed to breach. The killing in Genoa, a medieval seaport converted into a 21st-century citadel, is the first death during an anti-globalization demonstration since the movement tempestuously surfaced at a World Trade Organization meeting in Seattle in 1999.