The nation's industrial output rose sharply last month, the government reported yesterday. But the rise was mainly a bounceback from the April Teamsters' strike. The underlying pace of the economy remained relatively flat.

New figures from the Federal Reserve Board showed production of the nation's factories, mines and utilities climbed 1.3 percent in May-a sizable increase by any measure.

However, the gain barely offset a 1.4 percent decline that was posted after the Teamsters' strike slowed production of autos, trucks and steel. With this factored out, the production index remained virtually unchanged.

Moreover, output of consumer goods and construction supplies continued below their March levels despite the rebound in other sectors-pointing to a decided weakening in the economy from its pace in late 1978 and early this year.

The figures bolstered contentions by many key forecasters that the economy has begun to slow visibly and may be heading into a recession. The growth in employment last month was noticeably weak.

The rebound from the strike period was spread throughout key sectors of the economy. Output of consumer goods soared 1.8 percent over the month, with production of durable goods-influenced by autos-up 6.1 percent.

Production of business equipment rose 1.3 percent in May, after declining 0.9 percent in April. Output of construction supplies rose 0.6 percent, after plunging by 1.2 percent in April.

The revival in May brought the overall industrial production index to 152.1 percent of its 1967 average-a moderate 5.7 percent above its level of a year before. The index is linked closely to employment trends.

Auto assemblies soared by 19 percent in May to a new annual rate of 9.4 million units, returning to their March pace. However, the board said auto production is expected to be lower in June, reflecting a switch from big cars.

The May figures appeard generally to be in line with other key statistics published this past month, which have showed the economy slowing somewhat from the near-overheated pace earlier this year. CAPTION: Chart, Industrial Production. The Washington Post