The number of teen-aged American boys who use snuff and chewing tobacco has increased dramatically during the 1980s, raising concern among medical experts about a possible rise in rates of mouth cancer and other potential health consequences.

The figures showing the increase in teen-age use of smokeless tobacco products, especially in the South and West, were reported yesterday at the opening of a three-day conference on the health implications of the products. It is sponsored by the National Institutes of Health.

A 1985 study by the National Institute of Drug Abuse found 16 percent of males aged 20 or younger had used smokeless tobacco during the preceding year, compared with 11 percent of men aged 21 or older. The rates have more than doubled since 1975, when a survey of men over 21 found only 5 percent used chewing tobacco and 3 percent used snuff.

Twenty-two percent of male college students in 1985 were smokeless tobacco users, according to a national college survey by Elbert D. Glover, associate professor of community health at East Carolina University.

The surveys found use of smokeless tobacco by young women is low -- 2 percent nationally -- and has not changed significantly since 1970.

"It seems to be mainly a phenomenon of young white males in the South and West," said Beatrice A. Rouse, a NIDA epidemiologist. "Use among blacks and Hispanics is half that of whites."

She said researchers do not yet know whether the increased popularity of the products represents a passing fad or a trend that will continue as young users age.

"It depends how addicting smokeless tobacco is," she said.

Nicotine is absorbed into the bloodstream when tobacco is chewed, sucked or sniffed, and reaches levels similar to those found in the blood of smokers. Some studies suggest users who quit suddenly suffer withdrawal symptoms similar to those that accompany giving up smoking.

Medical experts view the rise in smokeless tobacco use with alarm because of research indicating that long-term "snuff dipping" (the holding of snuff between cheek and gums) leads to a heightened risk of mouth cancer.

White North Carolina women who dipped snuff had four times the risk of cancer of the mouth and throat than those who never used tobacco, according to a 1981 study by Deborah M. Winn, an epidemiologist at the National Center for Health Statistics. The longer the women had been users, the greater the risk. In women who dipped snuff for 50 years, there was a fiftyfold increase in mouth cancers.

Other research indicates that smokeless tobacco causes receding gums and changes in the lining of gums and cheeks.

Peer pressure, increased promotion of smokeless tobacco products and a widespread perception that the products are safer than cigarettes are among factors cited by researchers as possible explanations for the rise in teen-age use.

"The perception is that it's a safe alternative to smoking, and that influences choice," said Virginia L. Ernster, associate professor of epidemiology at the University of California at San Francisco School of Medicine.

However, Ernster said studies show that smokeless tobacco users are more likely than nonusers to become smokers.

Ernster said advertising for moist snuff, the type most favored by young people, has been increasing during the 1980s.

U.S. Tobacco, the major manufacturer of moist snuff, spent $1 million for television advertising of its products during the 1984 Winter Olympics. Television and radio promotion of smokeless tobacco was not affected by the 1971 law that banned such promotion of cigarettes.

Manufacturers of smokeless tobacco maintain that there are no scientifically proven health risks involved with using their products.

A statement by Michael J. Kerrigan, president of the Smokeless Tobacco Council, said the NIH conference "is unnecessary since the U.S. Congress is on the verge of enacting a law that mandates health warning labels on all smokeless tobacco products."

A bill requiring such labels was passed last month by the Senate.