JAPAN GIVES HINT THAT IT WILL ACT TO HALT YEN'S RISE
Bank of Japan's governor hints he may reverse course and act to halt three-month-long rise in value of Japanese yen before it chokes off country's fragile economic recovery and provokes further clashes with United States; vaguely worded announcement from Masaru Hayami, plus communique issued by finance ministers of Group of 7 largest industrialized nations, is enough to strengthen dollar slightly and weaken yen; just last week Hayami and central bank defied Japanese politicians and Washington by refusing to stop rise in yen's value; Hayami's comments are important in part because Wall Street reacted badly to moves last week by Bank of Japan; future of American stock markets seem increasingly dependent on decisions of Japan's central bank, institution that operates by its own rules and market rationale (M)