Medicine has eradicated, or completely eliminated from Earth, just one infectious disease. It is smallpox, a horror that killed millions over the centuries and was eradicated in 1977 after a long global vaccination effort.

In the following 10-year-period, people around the world saved an estimated $168 billion in medical costs, according to a 1998 congressional study. American taxpayers saved $17 billion.The figures, of course, ignore the human element. Wiping out smallpox has saved human beings pain, suffering and disfigurement that cannot be described in cold economic terms.

So why not reap a similar bounty and mount global efforts to push other infectious diseases into oblivion?

Efforts to eradicate or eliminate other infectious disease are under way. The World Health Organization has identified seven diseases as candidates for eradication or elimination.

The diseases on WHO's hit list are polio, measles, leprosy, Chagas' disease, dracunculiasis, onchocerciasis and lymphatic filariasis. The last four are parasitic diseases that occur mainly in developing countries.

"Eradicate" means to wipe out a disease so that zero cases occur and nobody needs to worry about catching it. "Eliminate" means reducing the number of cases to zero in a specific geographic area or reducing the number of cases to a level so low that the disease no longer poses a major public health problem.

Target dates range from the year 2000 for eradication of polio and elimination of leprosy to 2010 for eradication of measles and 2030 for elimination of filariasis.

WHO estimates that it will cost about $7.5 billion to deal with the diseases on its hit list. Most cases of these diseases occur in poor developing countries. Much of the cost thus would be paid by donor countries, like the United States.

Yet the study, conducted by the U.S. General Accounting Office, concluded that beating these diseases would save substantial amounts of money in the United States.

In 1997, Americans spent about $300 million on domestic control programs for polio, measles and leprosy. Another $91 million went to foreign aid programs for control of all seven diseases. Eradication of polio alone would save Americans $230 million spent on vaccination and other control measures in the United States and $74 million on overseas programs.

Health experts picked the diseases for two reasons: There was enough scientific knowledge to tackle the disease and enough political support in both the donor and recipient countries.

Other diseases long have been candidates for the eradication-elimination hit list, including several that are a big menace in the United States.

Consider, for instance, a 1993 report from the International Task Force for Disease Eradication (ITFDE), prepared by experts from WHO, the U.S. Centers for Disease Control and Prevention and other agencies.

ITFDE concluded it is technically possible to eradicate mumps, rubella (German measles) and Hib with vaccination programs. Hib is a bacterial infection that is the most common cause of childhood meningitis) and to eliminate hepatitis B.

ITFDE said hepatitis B, a viral infection that can lead to liver cancer, could be eliminated. Cost savings in the United States alone would run into the billions of dollars per year, experts say.