The nation's unemployment rate held steady in December while job growth rebounded, the government reported yesterday, heightening the current confusion over how the economy is performing.

The Labor Department's monthly survey showed the jobless rate last month at 5.9 percent of the work force, up a scant 0.1 percentage-point from November's level. The increase was too small to be statistically significant.

As the same time, the total number of jobs in the economy grew by a respectable 304,000 -- more than doubled the 134,000 rise recorded in November -- while industry payrolls swelled by 317,000 up from 127,000 the previous month.

Meanwhile, the Commerce Department reported that retail sales surged a hefty 1.1 percent in December -- evidence that consumers continued their spending spree through the Christmas shopping season.

The combination of figures appeared on the surface to fly in the face of predictions that the economy is sliding into a recession. There were expectations as late as a month ago that unemployment would begin rising now.

Nevertheless, economists continued to hew to their forcasts that the downturn would become visible during the first three months of this year and last well into the summer or early fall.

Current predictions are that the jobless rate will rise to about 7.5 percent or higher by autumn, as the slump in the housing and auto industries spreads to other sectors of the economy.

The jobless rate has been hovering at just under 6 percent for about 18 months. The December figure brought the average unemployment rate for all of 1979 to 5.8 percent, its lowest level in five years.

The rebound in new job growth came as a surprise to some economists. There had been some layoffs in the auto industry and in some other sectors, but many of these plants had reopened when the job survey was taken.

However, analysts caution privately that in large numbers of these cases the companies resumed their layoffs early in January, a factor which could push the jobless rate up in this month's survey, to be taken next week.

Economists did point to one worrisome sign in the December report -- a sizable jump in the number of persons who were forced to take part-time jobs for economic reasons. That figure often is an early indicator of rising unemployment.

However, other closely-watched employment signals were bullish: The length of the average work week rose further in December. And overtime levels at factories edged up over the month.