WHITE rice is tasteless, so most Westerners think. But Japanese find a world of flavor in every grain and they will describe at length the difference in texture and stickiness that distinguish a good brand from the rest.Although most Japanese have never tasted American brands, many doubt that a country for which rice is not a staple food can produce rice that will meet their tastes. But the bad image, some expatriates say, is what keeps Japanese consumers from pressing their government to open the nation's rice market to imports. "When I tell my visitors from Japan that what they are eating is American rice, all of them say, 'Hey, this is delicious, says Ryuichi Tezuka, a businessman who came to New York from Tokyo about a year ago. But not all US rice is good, he quickly adds. The rice he buys is from Korean grocery stores near his apartment and comes in bags with Japanese writing blazoned across them. The only English is at the bottom, in small print: "Made in the U.S.A." The rice is specially produced for Mr. Tezuka and other Japanese here from the grain known as M-401, a medium-size grain that Japanese strongly prefer to America's more common long-grain variety. M-401 was developed in California in 1981. M-401 and another high-quality grain, Kokuho Rose, have come to dominate sales to expatriates and to Japanese- and Korean-Americans. Ikuo Yamashita, a manager at Yaohan, a Japanese supermarket in New Jersey, says American and Japanese farming methods differ sharply: "American farmers fly over with a plane and drop seeds.... But Japanese farmers, instead of planting, say, 500 [seeds], plant 100. Rice makes men strong. But if you plant 500, they will be weak. Japanese farmers also use plenty of water. They're very careful." But the US-grown rice at Yaohan often gets higher marks from shoppers than the rice available in Japan. "California rice is better," says Junko Watanabe, a member of the Japanese UN Mission. "In Japan, the rice goes through a long distribution system and often comes out old." Convinced that discerning consumers in Japan need just a taste of American rice to win them over, representatives from the US Rice Council went to Japan in March with bags of California-grown Japanese rice to attend an international food fair. But Japanese officials sent them packing, citing the Food Control Law, to keep out even small samples of foreign rice.