By John S. McClenahen Three years ago, Asia was in the throes of an economic crisis, brought on by overly exuberant investment and punctuated by the mid-1997 collapse of Thailand's currency, the baht. Could it be happening again? Probably not, although Japan's current economic performance is plenty worrisome. Indeed, the world's second-largest economy may actually be contracting during this first half of 2001, says Singapore-based William Belchere, a member of Merrill Lynch & Co.'s global economic research team. By September, he believes, the yen, the Japanese currency, will have weakened to an exchange rate of 140 against the U.S. dollar. There are well-placed worries about lower Japanese demand for imports of manufactured goods and for less Japanese foreign direct investment in other areas of Asia. Nevertheless, Belchere's judgment is that Asia, outside of Japan, is "now passing through the worst part of its slowdown. The question is really when and how strong is the eventual recovery likely to be."