ByJohn S. McClenahen American consumers keep spending and pretty soon, it would seem, manufacturers' inventories should be low enough that production will have to ramp up to meet demand. Individual income-tax rebate checks "should help boost consumer spending going forward," suggests Gerald D. Cohen, a senior economist at Merrill Lynch & Co., New York. "As a result, consumer spending looks like it will climb at around [a] 2.5% pace in the third quarter." In July, the first month of 2001's third quarter, consumer spending rose 0.2% to an inflation-adjusted annual rate of $6.5 trillion, the U.S. Commerce Dept.'s Bureau of Economic Analysis reported Aug. 30. Growth in expenditures for services and non-durable goods more than offset a vehicle-driven 0.1% decline in outlays for durables.