By John S. McClenahen With the Commerce Department now reporting that U.S. GDP grew at an inflation-adjusted annual rate of 4% in this year's third calendar quarter, up nearly a percentage point from its 3.1% original estimate, the contrast with the apparent slow growth rate of the current quarter is much greater than expected. Merrill Lynch & Co., New York, for example, is forecasting just 1.5% growth in GDP this quarter, nearly as low as the 1.3% recorded in this year's second calendar quarter. With more inventory rebuilding, a higher level of housing construction and stronger exports than anticipated, the latest calculation of third-quarter GDP growth rate exceeded the 3.7% that economists generally expected. "Two-thirds of the upward revision to . . . GDP growth owed to higher inventories," figures Maury Harris, chief U.S. economist at UBS Warburg LLC, New York. But by the end of the third quarter in September, the U.S. economy was fading, he notes. "This sets up the current quarter for a slim 1.8% gain," says Harris. "Indeed, we think that the risks lie on the low side of that pace." That would put him closer still to Merrill Lynch's forecast. The Commerce Department expects to publish its first official take on fourth-quarter GDP on Jan. 30, 2003.