By Maggie Fox, Health and Science Editor

WASHINGTON, Oct 31 (Reuters) - Television ads that tobacco companies say are designed to discourage teenagers from smoking do no such thing, and some may actually encourage youths to smoke, researchers reported on Tuesday.

Their study of more than 100,000 U.S. teenagers show the ads may do more harm than good, the researchers wrote in the American Journal of Public Health.

"This study provides more proof that the tobacco industry is all smoke and mirrors," said M. Cass Wheeler, Chief Executive Officer of the American Heart Association.

"The tobacco industry is addicted to lying and in truth wants our kids to become addicted to tobacco. If they were serious about reducing smoking rates, they would stop spending $15 billion a year to promote their deadly products."

Melanie Wakefield of the Cancer Council Victoria, in Melbourne, Australia and colleagues at the University of Illinois at Chicago and the University of Michigan got television viewing data from Nielsen Media Research.

They looked at the reach and frequency of tobacco company-sponsored ads and whether they were seen by 12-year olds to 17-year olds in the largest 75 U.S. media markets, covering close to 80 percent of all U.S. households, from 1999 to 2002.

They then looked at surveys of 8th, 10th and 12th graders in 48 states collected in the same period for a study on tobacco use and beliefs at the University of Michigan.

The data showed no correlation between frequency of the industry's anti-smoking ads and actual or intended smoking by the teens.

"This research provides the clearest evidence to date that tobacco-sponsored ads don't work," Wakefield, also with the University of Illinois, said in a statement.

"Tobacco-sponsored ads targeted at youth have no impact and those targeted at parents seem to have an adverse effect on students who are in their middle and later teenage years."

DELAYING BUT NOT PREVENTING

The researchers noted that cigarette giant Philip Morris <MO.N> launched a national $100 million television "Think. Don't Smoke" campaign in December of 1998.

"Lorillard Tobacco Company also launched a U.S.-televised youth smoking prevention campaign with the slogan, 'Tobacco is Whacko if You're a Teen'," they added. Lorillard is owned by Loews Group <LTR.N>.

They noted that in one tobacco trial, Carolyn Levy, director of Philip Morris youth smoking prevention programs, "admitted that the aim of their programs was to delay smoking until age 18" -- not to prevent teens from ever smoking.

In the survey, teens living in markets where many parent-oriented ads aired were less likely to remember having seen such an ad, and were more likely to say they might smoke in the future.

"It is conceivable that tobacco company smoking prevention ads could have even greater adverse effects on youth smoking behavior than suggested by this study," they wrote.

The Campaign for Tobacco-Free Kids said seven U.S. states had initiatives on the ballot next week in nationwide elections that would raise tobacco taxes, fund tobacco prevention programs, and require smoke-free workplaces and public places.

"Just as they have sought to mislead the public with their fake prevention programs and other deceptive tactics, the tobacco companies are now spending tens of millions of dollars to mislead voters and defeat these ballot initiatives," said William Corr, Executive Director of the group.