Chinese and Indian drug makers have taken over much of the global trade in medicines and now manufacture more than 80 percent of the active ingredients in drugs sold worldwide. But they had never been able to copy the complex and expensive biotech medicines increasingly used to treat cancer, diabetes and other diseases in rich nations like the United States — until now.

These generic drug companies say they are on the verge of selling cheaper copies of such huge sellers as Herceptin for breast cancer, Avastin for colon cancer, Rituxan for non-Hodgkin’s lymphoma and Enbrel for rheumatoid arthritis. Their entry into the market in the next year — made possible by hundreds of millions of dollars invested in biotechnology plants — could not only transform the care of patients in much of the world but also ignite a counterattack by major pharmaceutical companies and diplomats from richer countries.

Already, the Obama administration has been trying to stop an effort by poorer nations to strike a new international bargain that would allow them to get around patent rights and import cheaper Indian and Chinese knock-off drugs for cancer and other diseases, as they did to fight AIDS. The debate turns on whether diseases like cancer can be characterized as emergencies, or “epidemics.”

Rich nations and the pharmaceutical industry agreed 10 years ago to give up patent rights and the profits that come with them in the face of an AIDS pandemic that threatened to depopulate much of Africa, but they see deaths from cancer, diabetes and other noncommunicable diseases as less of an emergency and, in some cases, the inevitable consequence of better and longer living.