* Takeshi Araki, 78, the former mayor of Hiroshima, Japan, who made a mission of urging the world to abolish nuclear weapons, died yesterday of pneumonia. The four-term mayor became known for the official appeals he made to the world every Aug. 6 to ban nuclear bombs. On that day in Hiroshima in 1945, he lived through the world's first atomic bomb attack, the first of two by United States forces that led to Japan's surrender in World War II.