People who switch from regular cigarettes to brands marketed as "low tar" or "light" tend to smoke more and inhale more deeply to get the same nicotine, eliminating any health benefit, the National Cancer Institute said Tuesday.

Dr. David Burns, the study's lead author, said the report supersedes a 1981 recommendation by the U.S. surgeon general that smokers switch to light cigarettes if they can't quit.

"That was our recommendation at that time. It turns out to have been a bad mistake," said Burns, who helped edit the surgeon general's report.

Burns and his colleagues spent the past three years reviewing five decades worth of data examining low-tar cigarettes. They found that some people who switched to low-tar brands smoked more to get the same amount of addictive nicotine, since the ratio between tar and nicotine generally remains the same in all cigarettes.

Tar is a carcinogen that is produced when tobacco is burned. It helps deliver nicotine to smokers. Low-tar cigarettes are supposed to have less than 15 milligrams of tar.

The study found that people who switched to light brands typically thought they were reducing their risk of developing smoking-related disease and that tobacco companies contributed to those assumptions through advertising and marketing campaigns.

"The results of the review are clear. There is no convincing evidence the changes in cigarette design over the last 50 years have reduced the disease burden produced by cigarettes," Burns said.

The study also found cigarettes that yielded low tar and nicotine levels when tested on Federal Trade Commission machines had higher levels when smoked by people, partly because people take larger puffs and smoke more of the cigarette. In addition, smokers can inadvertently cover ventilation holes in the filter designed to lower tar levels.

"When they do that, they get a full dose of tar and they don't have any risk reduction," Burns said.

Sharon Boyse, the director of research for Brown & Williamson Tobacco Corp., the nation's third-largest tobacco company, did not dispute those findings. But she said it's important to note that, if smokers are aware of how they smoke, light cigarettes can deliver less tar than regular ones.

The World Health Organization is sponsoring talks on an international convention meant to reduce smoking and tobacco-related disease, which kills 4 million people each year worldwide. One of the provisions is for a ban on terms such as mild and low-tar.

John Kirkwood, chief executive officer of the American Lung Association, said health groups sent letters Tuesday to members of Congress and the Bush administration calling for Food and Drug Administration regulation of tobacco. They also sent letters to tobacco companies urging them to voluntarily stop using low-tar labels on their cigarettes.

Boyse said Brown & Williamson opposes such a ban. A spokesman for Philip Morris Inc., the nation's largest tobacco company, said the company would support greater regulation of the terms "low tar" and "light."

The effort to produce and market low-tar cigarettes gained momentum in the 1960s, after public health advocates said cigarettes with less tar would produce less cancer. But studies by the American Cancer Society in the 1960s and 1980s found lung cancer death rates among male and female smokers rose even as tar levels in cigarettes dropped by 60 percent.

The NCI report says public health officials who backed the production of light cigarettes failed to take into account the highly addictive nature of nicotine and the difference in actual tar and nicotine levels taken in by people and testing machines.

Attending a news conference to announce the report were former U.S. Surgeon General C. Everett Koop and gun-control activist Sarah Brady, who is battling lung cancer. Through tears and coughs, Brady said she was among those who switched to light cigarettes thinking they would be better for her.

"Never allow yourself to get into the predicament that I'm in," said Brady, who has been unable to quit smoking. "The switch to low-tar lured me into a feeling of false security."