LONDON, Jan 15 (Reuters) - U.S. regulators are proposing

to cap the amount of nicotine in cigarettes at non-addictive

levels, in a potential world-first that could curb smoking and

hit tobacco industry earnings.

The U.S. Food and Drug Administration (FDA), which regulates

products containing nicotine, a highly addictive drug, first

raised the idea of such a cap in 2018. It said this would save

lives by preventing smoking-related disease and death, by taking

away the chemical that keeps smokers hooked.

On Wednesday, it proposed capping the level of nicotine at

0.7 milligrams per gram of tobacco in cigarettes and other

combustible tobacco products, such as cigars and roll your own

tobacco. Alternatives like vapes, nicotine pouches and heated

tobacco would not be affected by the cap.

That would mean cigarettes would no longer deliver the

nicotine hit desired by many smokers, encouraging them to quit

or switch to alternatives, while young people could be less

likely to take up smoking in the first place.

"This proposal allows for the start of an important

conversation about how we meaningfully tackle one of the

deadliest consumer products in history and profoundly change the

landscape of tobacco product use in the United States," said FDA

Center for Tobacco Products director Brian King.

The agency's modelling predicted such a rule could prevent

48 million youth or young adults from starting smoking, and more

than 12.9 million people who smoke would give up within one year

of it coming into effect. That would rise to 19.5 million within

five years, it said.

That would threaten the profit engine of large tobacco

companies like British American Tobacco ( BTI ) and

Marlboro-maker Altria ( MO ). While they are growing sales from

alternatives like vapes, the vast majority of their revenues

still come from tobacco.

They did not immediately respond to a request for comment.

The FDA's proposal is "truly game-changing", said Yolanda

Richardson, President and CEO of the Campaign for Tobacco-Free

Kids, urging President-elect Donald Trump to finalise and

implement the rule. He takes office on Jan. 20.

The public will have until September to provide comments on

the proposal, the FDA said.