The boom in America's economic growth during the first three months of 1981 -- the biggest quarterly increase since the economy grew 9 percent in the second quarter of 1978 -- was even bigger than first thought. The gross national product (the measure of the nation's total output of goods and services) grew 8. 6 percent after adjustment for inflation during the first quarter, the Commerce Department reported. This was the second time the GNP figure has been raised in the course of normal revisions, made as more information becomes available.
Economists expect much slower growth during the April-June quarter when the figures become available.