The closely watched U.S. economy is not in recession. Last week's preliminary Commerce Dept. read of second quarter 1998 economic activity showed a 1.4% advance -- very modest, but positive growth, nevertheless. For the first six months of this year, the U.S. economy grew at an inflation-adjusted rate of 3.5%. And Merrill Lynch & Co. Inc. is forecasting 2% to 2.5% growth during the year's final six months. But it and other analysts could be underestimating the impact of Asia's continuing financial and political crisis on the U.S. economy. With Asia largely responsible, net exports cut 2.5 huge percentage points from gross domestic product growth between January and June. The loss could be greater than the one percentage point now being projected for the second half of this year.