U.S. workers' productivity increased 1.4 percent last year, the government reported yesterday, an improvement that nonetheless revived doubts about economic projections at the heart of President Bush's spending plans.</br></br>The 1.4 percent gain in nonfarm business productivity was up from 0.8 percent in 1987 and matched the average 1.4 percent annual gain experienced since the end of the 1981-82 recession, the Labor Department reported.</br></br>Increased productivity-getting each worker to produce more each hour that he or she is on the job-is vital to economic growth without inflation, particularly given the current squeeze in the labor market.</br></br>Total business productivity, including farming, fell at a 2 percent annual rate in the fourth quarter of 1988 because of a drop in farm productivity. Manufacturers reported a 3.2 percent increase in productivity last year, down from 3.4 percent in 1987, the Labor Department said.</br></br>In his final budget, former president Ronald Reagan forecast a 1.2 percent productivity gain in 1989, a 1.8 percent rise in 1990, a 2 percent jump in 1991 and 2.1 percent increases the next three years.