The nation's factories again slashed their operating schedules sharply last month, this time to 78.9 percent of total capacity, the government reported yesterday.

The May figure, down 2 percentage points from April's 80.9 percent, marked the lowest rate at which factories have operated in the United States in more than four years.

Last month's decline, the fourth drop in a row and yet another sign of the fast-deepening recession, followed a 2.2 percentage point plunge in April and an 0.7 percentage point dip the previous month.

Since the recession began last January, the index has plummeted 5.5 percentage points. A year ago, U.S. factories were operating at between 86 percent and 87 percent of capacity.

Yesterday's figures paralleled other major indicators recently showing the economy. Earlier, the slump had been concentrated primarily in the auto and housing industries.

Other government reports recently have shown industrial production plunged 2.1 percent in May while the nation's overall jobless rate soared to 7.8 percent -- the highest since November 1976.

The May utilization rate of 78.9 percent was the lowest since February 1976, when the economy was still recovering from the 1974-75 recession -- its deepest slump since 1938.

Yesterday's statistics, compiled by the Federal Reserve Board, also showed cutbacks in operating rates for other major group of industries.

The utilization rate for advanced processing industries, for example, dropped to 79.5 percent in May from 80.8 percent in April, while that for primary processing industries fell to 77.8 percent from 80.9 percent.