But beginning in the 1980s, the Chinese government invested huge sums in penicillin fermenters, “disrupting prices around the globe and forcing most Western producers from the market,” said Enrico Polastro, a Belgian drug industry consultant who is an expert in antibiotics.

Part of the reason these plants went overseas is that the F.D.A. inspects domestic plants far more often than foreign ones, making production more expensive in the United States.

“U.S. companies are more regulated and are under more scrutiny than foreign producers, particularly those from emerging countries. And that’s just totally backwards,” said Joe Acker, president of the Synthetic Organic Chemical Manufacturers Association. “We need a level playing field.”

The Bush administration spent more than $50 billion after the 2001 anthrax attacks to protect the country from bioterrorism attacks and flu pandemics; some of that money went to increase domestic manufacturing capacity for flu vaccines.

Even so, officials have said that during a pandemic the United States would not be able to rely on vaccines manufactured largely in Europe because of possible border closures and supply shortages. And the situation is similar with antibiotics like penicillin; researchers have found that during the 1918 flu pandemic, most victims died of bacterial infections, not viral ones.

The Centers for Disease Control and Prevention has a stockpile of medicines with enough antibiotics to treat 40 million people. If more are needed, however, the nation lacks the plants to produce them. A penicillin fermenter would take two years to build from scratch, Mr. Polastro said.

Dr. Yusuf K. Hamied, chairman of Cipla, one of the world’s most important suppliers of pharmaceutical ingredients, says his company and others have grown increasingly dependent on Chinese suppliers. “If tomorrow China stopped supplying pharmaceutical ingredients, the worldwide pharmaceutical industry would collapse,” he said.