Sales of imported vehicles in Japan rose a robust 29% last year to 388,162, says the Japan Automobile importers Association. But more than two-thirds (263,593) of those were either produced in Germany or built in Japanese automakers' North American or European assembly plants. Sales of U.S.-built GM,and vehicles in Japan increased 1 1.4% from 1994 to 38,150, or roughly 1 0% of the import total. The Big Three want to sell 400,000 vehicles annually in Japan by 2000. By the end of 1997 they plan to introduce nine new right-hand-drive models in Japan, including Chrysler's Neon, Ford's Taurus station wagon and Saturn. Imports accounted for 7.5% of Japan's new-car market, a share that could double over the next three years, predicts analyst Enda Clarke of Kleinwort Benson Securities in Tokyo.