This is bad news for the nation’s workers, who are already facing one of the bleakest labor markets in recent history. Temporary employees generally receive fewer benefits or none at all, and have virtually no job security. It is harder for them to save. And it is much more difficult for them to develop a career arc while hopping from boss to boss.

“We’re in a period where uncertainty seems to be going on forever,” said David Autor, an economist at the Massachusetts Institute of Technology. “So this period of temporary employment seems to be going on forever.”

This year, companies have hired temporary workers in significant numbers. In November, they accounted for 80 percent of the 50,000 jobs added by private sector employers, according to the Labor Department. Since the beginning of the year, employers have added a net 307,000 temporary workers, more than a quarter of the 1.17 million private sector jobs added in total.

One worker who has been forced to accept temporary jobs is Jeffrey Rodeo, 43, who was laid off 14 months ago from his job as an accounting manager at a produce company in Sacramento. He has applied for nearly 700 full-time positions since then, but has yet to receive an offer. Meanwhile, to stay afloat and keep his skills fresh, he has worked on short-term stints at four different employers.

Mr. Rodeo figures his peripatetic work life will last at least another year. “Companies are being more careful,” he said. “It just may take longer to secure a permanent position.”

To the more than 15 million people who are still out of work, those with temporary jobs are lucky. With concerns mounting that the long-term unemployed are becoming increasingly unemployable, those in temporary jobs are at least maintaining ties to the working world.

The competition for them can often be as fierce as for permanent openings, and there are still far too few of them to go around. Indeed, the relative strength in temporary hiring has done little to dent the stubbornly high unemployment rate, which rose to 9.8 percent in November.

“With business confidence, particularly in the small business sector, extremely low,” said Ian Shepherdson, chief United States economist at the High Frequency Economics research firm, “it’s not surprising that permanent hiring is lagging behind.”

The landscape two or three years from now might look quite different, of course. Many economists and executives at temporary agencies say there are signs that more robust permanent hiring is coming in the new year. Business confidence is up, and temporary agencies report that the percentage of interim workers who have been offered full-time jobs is also up from last year.

Nevertheless, there are signs that this time around, the economy could be moving toward a higher reliance on temporary workers over the long term.

This year, 26.2 percent of all jobs added by private sector employers were temporary positions. In the comparable period after the recession of the early 1990s, only 10.9 percent of the private sector jobs added were temporary, and after the downturn earlier this decade, just 7.1 percent were temporary.