(FORTUNE Magazine) – The tiny Pacific island of Okinotorishima at the extreme southern end of the Japanese archipelago gives new meaning to the term ''flyspeck.'' At high tide it consists of two coral rocks 10 and 16 feet wide. Little Okinotorishima looms large to Japan. It stakes a territorial claim amounting to 154,440 square miles where Japan has exclusive fishing rights. Without it, the archipelago's southern extreme would be Iwo Jima or Oki Daitoshima, each about 375 miles closer to the main islands. Three years ago the government decided to do something about the typhoon- battered island, which was eroding into nothingness. To save their molehill, the Japanese enclosed it in a mountain: a concrete ring with a seawall built of 9,900 steel blocks. None of the man-made materials could touch the natural formation because that would have made it an ''artificial island'' and unacceptable as a national boundary. After losing the island in 1945 and regaining it in 1968, the Japanese have now spent $200 million to save it -- many times the annual revenues of the Japanese fishermen who ply the surrounding waters. - S.S.