But a Chinese official disputed the assertion that the contaminant found in the drug, heparin, caused any deaths and insisted that his country’s inspectors be allowed to inspect the American plant where the finished heparin vials were made. He said any future agreement to allow American inspections of Chinese firms should be reciprocal.

“We don’t have a strong evidence to show that it is heparin or its contaminant that caused the problem,” said the official, Ning Chen, second secretary at the Chinese Embassy.

Mr. Chen said that illnesses associated with contaminated heparin had occurred only in the United States, which he said suggested that the problem arose in this country.

Dr. Janet Woodcock, director of the Food and Drug Administration’s drug center, said that German regulators uncovered a cluster of illnesses among dialysis patients who took contaminated heparin. She said Chinese officials had conceded that heparin produced in their country contained a contaminant, though they say it was not connected to the illnesses.

“Heparin should not be contaminated, regardless of whether or not that contamination caused acute adverse events,” Dr. Woodcock said. “We are fairly confident based on the biological information that we have had that this contaminant is capable of triggering these adverse reactions.”

The dispute is a sign of growing tensions between China and the United States over the safety of Chinese imports. China has in recent years exported poisonous toothpaste, lead-painted toys, toxic pet food, tainted fish and now, contaminated medicine.

Bills to require far more aggressive inspections of Chinese products and companies are being proposed by members of Congress. Hearings are scheduled for Tuesday in the House and Thursday in the Senate.

China has lurched between defensiveness and cooperation on issues of product safety. Last year, it initially blocked the F.D.A. from investigating tainted pet food and accused foreign forces of exaggerating the issue. Then in July, China said that it had executed its former top food and drug regulator for taking bribes and promised reforms.

The F.D.A. sent a warning letter on Monday to Changzhou SPL, the Chinese plant identified as the source of contaminated heparin made by Baxter International in the United States. It warned that the plant used unclean tanks to make heparin, that it accepted raw materials from an unacceptable vendor and that it had no adequate way to remove impurities.

Heparin is made from the mucous membranes of the intestines of slaughtered pigs that, in China, are often cooked in unregulated family workshops. The contaminant, identified as oversulfated chondroitin sulfate, a cheaper substance, slipped through the usual testing and was recognized only after more sophisticated tests were used.

The F.D.A. has identified 12 Chinese companies that have supplied contaminated heparin to 11 countries — Australia, Canada, China, Denmark, France, Germany, Italy, Japan, the Netherlands, New Zealand and the United States. Deborah Autor, director of compliance at the F.D.A.’s drug center, said the agency did not know the original source of all the contamination or the points in the supply chain at which it was added.

Officials have discovered heparin lots that included the cheap fake additive manufactured as early as early as 2006, although a spike in illnesses associated with contaminated heparin began in November and persisted through February, officials said.

Separately, the Government Accountability Office will release a report on Tuesday showing that the F.D.A. would need to spend at least $56 million more next year to begin full inspections of foreign plants. It would need to spend at least $15 million annually to inspect China’s drug plants every two years, which is the domestic standard.

Bush administration officials have acknowledged problems associated with poor inspection of overseas plants and have plans to improve the situation. But President Bush’s budget does not provide the F.D.A. with funds to hire more inspectors.

At its present inspection pace, the F.D.A. would need at least 27 years to inspect every foreign medical device plant that exports to the United States, 13 years to check every foreign drug plant and 1,900 years to examine every foreign food plant.

Proposals circulating on Capitol Hill would increase the agency’s financing and charge domestic and foreign manufacturers fees to pay for inspections.

“Even the Bush administration seems to understand the potential peril that these foreign firms pose, but they offer only vague plans to address the problems and they refuse to spend more than a fraction of the money needed to protect the public,” said Representative John D. Dingell, a Michigan Democrat who leads the House Committee on Energy and Commerce.

The F.D.A. has announced plans to open inspection offices in three Chinese cities, but the agency has yet to get permission from the Chinese government. Mr. Chen said any inspection agreement should be reciprocal. “Will the U.S. government accept the Chinese F.D.A. to set up in the United States?” he said.

Dr. Woodcock said the Chinese had agreed to test heparin lots before allowing them to be exported. But Dr. Moheb Nasr, director of the drug agency’s office of new drug quality assessment, said that the Chinese test might not be sensitive enough to identify the contaminant.

Dr. Woodcock assured patients, however, that all heparin supplies in the United States had been tested with the most sensitive assays and had been found to be uncontaminated.

Scientific Protein Laboratories and Changzhou SPL said the company regretted the agency’s decision to send a warning letter that, it said, did not reflect the company’s current safety practices. The company said it had no way of detecting a contaminant present in heparin supplies throughout China.

Baxter International, which bought heparin ingredients from SPL and sold the finished drug in the United States, said that its tests confirmed that the contaminant could cause illness. It disputed the F.D.A.’s analysis that its product was linked with 81 deaths, saying it had identified only 5 in which its product “may have contributed to the adverse outcome, though there is not yet enough medical data available to draw a firm conclusion that the reaction caused the death.”

Deaths linked to the drug may have been concentrated in the United States because American doctors may be more likely to use large, quickly infused amounts of the drug, said drug officials. Also, the F.D.A. may track serious side effects better than its counterparts abroad.

The number of suspicious deaths in the United States linked to the blood thinner heparin has risen to 62 from 19, with most of them reported this past December, January and February, according to the first detailed analyses of heparin fatalities by the Food and Drug Administration.

The F.D.A. is still investigating whether those deaths and hundreds of allergic reactions were caused by a heparinlike contaminant made in China that was added to the drug somewhere during the manufacturing process.

The drug agency defined suspicious deaths as those involving one or more allergic reactions or a drop in blood pressure. There have been no reports of deaths since the end of February, after Baxter International recalled heparin made with ingredients from a Chinese supplier.

The agency’s Web site reported Tuesday that the 62 deaths covered a 14-month period that began in January 2007. In comparison, the agency said, there were three suspicious deaths involving heparin in all of 2006.

The F.D.A. had earlier identified the contaminant as a chemically altered substance that slipped through standard testing screens because it mimicked heparin. The agency was able to spot the additive only by using a more sophisticated test.

Investigators have not yet established how or why the additive, called oversulfated chondroitin sulfate, ended up in heparin, though the fact that it is cheaper to make than the actual drug points to the possible involvement of counterfeiters.

In addition to Baxter, companies that have recalled heparin products made with Chinese ingredients include Covidien, formerly Tyco Healthcare, and B. Braun. Both Covidien and Braun said that they had received no reports of adverse reactions from the heparin and that the recalls had been undertaken merely as a precaution.

Similar recalls of the drug have occurred in Germany, Denmark, France, Italy and Japan.

Heparin is made from the mucous membranes in pig intestines. It is commonly used in dialysis and in many types of surgery.

Drug regulators in China, the world’s biggest supplier of heparin ingredients, have said they are tightening supervision over production of the drug, which involves thousands of small family workshops that gather and treat the raw material from pig intestines.