BY THE YEAR 2020, tobacco is expected to kill more people than any single disease, according to a recent study by public health experts. Smoking in the United States has declined, but U.S. companies remain the world's most successful cigarette manufacturers -- and their exports continue to increase. The harm they have brought to Americans, in other words, they are now seeking to visit many times over throughout the world.

So it is appropriate that the world's nations are mobilizing in an unprecedented way to fight this unique threat to the public health. "It seems only right that we focus on tobacco," says Gro Harlem Brundtland, a former prime minister of Norway and now head of the World Health Organization. "At the turn of a century packed with achievements in science and medicine, tobacco stands out as an area of appalling neglect."

WHO, for the first time in its history, is promoting a treaty -- specifically, a treaty to govern tobacco and the tobacco industry. Nations have negotiated protocols on trade and arms control and the environment, but never a legally binding convention on health. But in late May, 191 countries attending the World Health Assembly voted to begin negotiations on a Framework Convention on Tobacco Control.

The talks won't be easy, and unfortunately they're not scheduled for completion until 2003. They shouldn't be regarded as a substitute for national action. But the possible benefits already are clear. A treaty could set standards for advertising, labeling, control of sale to children and similar issues. Those standards in turn could give governments needed ammunition against the lobbying of multinational tobacco companies.

In addition, without international cooperation, those companies can undermine many national attempts to control tobacco. Advertising can flow across borders on satellite television networks. Smuggling can undercut a country's efforts to tax appropriately and to insist that packages carry strong warnings. An international treaty could deal with such issues and also could control duty-free sale of cigarettes and help promote alternative crops for tobacco farmers. And a WHO convention might help convince its sister agency, the World Trade Organization, that cigarettes do not deserve routine free-trade protection but rather should be regulated as the addictive and lethal products that they are.