Economic activity in the manufacturing sector expanded in May for the fourth consecutive month, while the overall economy grew for the 67th consecutive month, say the nation's supply executives in the latest Manufacturing ISM Report On Business.   ; The PMI rose to its highest level in the past 12 months. Both the New Orders and Production Indexes indicated growth. The ISM Inventories Index indicates that manufacturers are now in their 10th month of inventory reduction. A major concern of respondents is the rate of price increases covering a wide variety of commodities.