Japan has turned down a U.S. request to join in economic sanctions against Iran. "Given that the U.N. secretary general is still continuing his efforts (to mediate in the Iran-Iraq conflict). . . we think it is too early to take economic measures against Iran," Deputy Foreign Minister Ryohei Murata told U.S. Under Secretary of State Michael H. Armacost at a meeting in Tokyo. Japan, which imports virtually all its oil, buys about 7% from Iran. West Germany also has rejected the U.S. call for a trade embargo against Iran. President Reagan said the sanctions are warranted because of Iran's continued support for terrorism, attacks on U.S. forces and ships flying the U.S. flag, and refusal to abide by a U.N. resolution calling for a cease-fire in its war with Iraq.