The nation's efficiency in producing goods and services improved slightly in the fourth quarter of last year instead of taking a downturn as earlier estimated, the government said yesterday.

Based on revised figures last week for the gross national product, the Bureau of Labor Statistics said nonfarm productivity rose at an annual rate of 0.3 percent from October through December last year instead of declining 0.2 percent as reported in preliminary figures a month ago.

The revised figures showed output of goods and services by nonfarm businesses -- which account for about three-fourths of the nation's economic production -- rising by 5.6 percent, the largest increase in nearly two years, instead of 5.1 percent as reported in the preliminary figures.

The higher output reduced the annual increase in labor costs associated with each unit of goods or services from 3.7 percent to 3.1 percent, the bureau said.

The fourth-quarter changes had little impact on the productivity figures for all of 1987, raising the efficiency gains for the year a tenth of a percentage point from 0.8 percent to 0.9 percent and dropping the unit labor cost increases from 2.0 percent to 1.9 percent.

Under the revised figures, the showing is still the worst since 1982, when a recession depressed output so much that businesses were 0.6 percent less efficient than they had been in 1981.

Despite figures showing that hourly wages rose an average 2.8 percent last year, workers still lost 0.8 percent of their income for each hour they worked after taking inflation into account, according to the revised figures.

Manufacturing workers fared even worse, with nominal wage increases averaging 1.3 percent, which decreased their purchasing power after inflation by 2.2 percent for the year.

Productivity in manufacturing improved 3.3 percent over the year -- unchanged from the preliminary figures -- with output up 4.3 percent on only a 1 percent increase in the number of hours worked.

That combination dropped the labor costs associated with each product coming out of the nation's factories by an average 1.9 percent last year, the bureau said.