Similarly, the strong exports provide a stark reminder of how vulnerable this country could be to protectionist trade wars. The Doha round of world trade talks, which was supposed to result in the lowering of more trade barriers, has stalled. And last month China imposed punitive duties on imports of American large cars and sport utility vehicles, which total about $4 billion a year.

That move was seen as retaliation for United States requests that the World Trade Organization rule that Chinese subsidies for its solar and poultry industries violated international law. The Chinese denounced those requests as protectionist.

The American government denies that, of course. “Part of a foundation of a rules-based system is dispute settlement," said Ron Kirk, the United States trade representative, in an interview with Reuters after the Chinese announced the new tariffs. "That’s what we think is so important about the W.T.O. How China reacts to that is up to China. But I just cannot buy into the argument that our standing and protecting the rights of our exporters and workers is somehow igniting a trade war or being protectionist.”

Since employment in the United States hit its recent low, in February 2010, the economy has added 2.4 million jobs through November, of which 302,000 were in manufacturing. With government payrolls shrinking, and financial services jobs also fewer, manufacturing employment has played an important role in keeping the economy growing. It also is helping that construction employment appears to have hit bottom. In the first 11 months of 2011, it is up a small amount.

To be sure, the gains in manufacturing employment and exports have come after sharp declines during the recession and credit crisis. There are still 6 percent fewer manufacturing jobs than there were when President Obama took office at the beginning of 2009, and it seems very unlikely that he will be the first president since Bill Clinton, in his first term, to preside over growing manufacturing employment during a four-year term.

During George W. Bush’s two terms, the number of manufacturing jobs fell by 17 percent in the first four years and by 12 percent in the following four years. The number declined by 1 percent in Mr. Clinton’s second term.

The Institute for Supply Management survey of manufacturers has shown more companies planning to hire than to fire in every month since October 2009. That string of 27 months is the longest such string since 1972, but remains well behind the longest one, 36 months, which ended in December 1966.