The nation's surplus in merchandise trade in the April-September period rose 44.7 percent from a year earlier to 7.411 trillion yen, the largest since the same fiscal half of 1986, according to preliminary figures released Wednesday by the Finance Ministry.The September trade surplus alone expanded 45.6 percent from the same month last year to reach 1.548 trillion yen, marking the 18th consecutive month of increase on a customs-cleared basis, officials said.The economic boom being experienced in the United States and Europe pushed up exports, while Japan's deepening recession and falling international prices of crude oil dragged down imports, the Finance Ministry said.The pace of increase in the trade surplus should slow gradually because companies are moving their production bases overseas and economic stimulus measures are expected to take effect, the ministry said.Exports in the first half of fiscal 1998 rose 2.4 percent year-on-year for the ninth consecutive fiscal-half to 25.909 trillion yen. Imports fell 8.3 percent to 18.498 trillion yen, or the second fiscal-half decline in a row.The resultant 7.411 trillion yen surplus represented an increase for the third consecutive period, beginning in the first half of fiscal 1997.Japan ran a trade surplus with all three major regions. The surplus with the United States increased for the fourth straight semiannual period, rising 41.3 percent to 3.424 trillion yen. Exports grew 14.2 percent and imports slipped 0.3 percent.