For South Korea as a whole,that seems as much a prophecy as an ambition. Like Japan in the 1960s,the country is poised for an assault on the world' s export markets. Its surging $81 billion economy is churning out a flood of increasingly sophisticated products,from shoes,toys and telephones to video recorders and microprocessors. Korea's mighty conglomerates dominate Middle East construction,and they command key shares of the world' s shipbuilding,textile and steel industries.