Mayor Bloomberg is ramping up his international antitobacco campaign by pumping in an additional $250 million and by teaming up with a former chairman of Microsoft, Bill Gates, who is contributing $125 million to combat tobacco use.

The funds will target smoking in the developing world, with an emphasis on China, India, Indonesia, Russia, and Bangladesh.

Mr. Bloomberg’s funding will support projects that seek to raise taxes on tobacco, promote negative images of smoking, help people quit smoking, and protect nonsmokers from exposure to tobacco smoke.

The investment by the Bill and Melinda Gates Foundation includes a $24 million grant for the Bloomberg Initiative, with the rest of the $125 million going to support other efforts to combat smoking.

Mr. Bloomberg, who banned smoking from bars and restaurants in New York and in 2005 established a $125 million initiative to reduce tobacco use, said it made sense to combine his and Mr. Gates’s “muscle” and “access” to take on smoking and encourage others to join in their efforts.

“I hope you get a strong sense of optimism from all of us that smoking is an epidemic that can be stopped, and we welcome more people to get involved, because it will be a tough fight and a long-term fight, but a very important one,” Mr. Gates said.

One of the biggest challenges the philanthropists face is convincing national governments to take action against smoking, through smoking laws, tax increases, and public awareness campaigns.

More than a third of all cigarettes in the world are produced in China; 67% of the country’s male population smokes, while 8% of its tax revenues come from the tobacco industry.

Mr. Gates said the top government officials that he has spoken with told him they are confident the country’s antismoking laws will be expanded in the future. China has promised to host a “smoke-free” Olympics.

In February, a study by the World Health Organization that was paid for by Bloomberg Philanthropies found that tobacco could kill 1 billion people in the 21st century if urgent action isn’t taken.

A spokeswoman for Philip Morris International, Marija Sepic, wrote in an e-mail message that the tobacco company “believes that the issue of tobacco regulation needs to be an important focus for governments worldwide.”

She added: “We have consistently supported the harm reduction goals of governments and many in the public health community.”