By John S. McClenahen For the third consecutive month, Spain's index of leading economic indicators edged down in June. The one-tenth of a percentage point decline followed a one-tenth-percentage-point decline in May and a two-tenths-percentage-point decline in April, says the Conference Board, a New York-based business research group. Spain's leading index now stands at 135.4 (1990=100). "The growth rate of the leading index has slowed into the 1% to 2% range [annual rate], and the weakness has become more widespread," notes the Conference Board. "However, it is too soon to conclude that the upward trend in the leading index that has been under way for two years has ended."