“I reckon this will avoid tens of millions of deaths in my lifetime and hundreds of millions in my kids’ lifetimes,” he said.

Catherine Armstrong, a spokeswoman for British American Tobacco  one of the Western tobacco companies that focuses on sales to the third world  would not comment directly on the new initiative. But she said, “We have no problem with government organizations educating people on the risks of tobacco.”

A spokesman for Philip Morris, which makes Marlboro, the world’s most popular cigarette brand, said the company agreed that children should be kept from smoking but thought that raising cigarette taxes promoted smuggling and counterfeiting.

Mr. Bloomberg, founder of the financial news company bearing his name and creator of the Bloomberg Family Foundation, has long been known for his antipathy to tobacco. During his administration, New York has adopted several antismoking measures, including a ban on smoking in bars and restaurants, and significant increases in cigarette taxes.

The global campaign promises to be a struggle. Cigarettes not only are highly addictive and supported by huge advertising campaigns, they are also an important source of income for many foreign governments. In China and other countries, tobacco is a state-owned monopoly, and low- and middle-income countries collect $66 billion a year in tobacco taxes.

Only about 5 percent of the world’s countries have any antismoking measures like those the campaign envisions. But Dr. Peto said antismoking campaigns were already having some effects, even in countries where no-smoking signs are often ignored. He surveyed thousands of tobacco users in China in the 1990s  “before the government was taking it seriously,” he said  and found 4 percent who identified themselves as former smokers. Now, he said, 20 percent do.

In India, where people have long chewed tobacco but widespread smoking is more recent, Dr. Peto said he found almost no one who had quit. “India is where China was in the mid-1990s,” he said.