Youthful nicotine addiction may be growing.

The proportion of teenagers and young adults who smoke cigarettes daily has declined in the United States over the past 20 years, thanks in no small part to a public health campaign to discourage tobacco use. At the same time, however, nicotine addiction has widened its grip among those young people who do smoke, a new study finds.

Daily cigarette smokers aren't necessarily hooked on nicotine. But for people ages 24 and younger, the rate of addiction among regular cigarette smokers has increased even as the overall popularity of smoking has dropped, reports a team led by psychologist Naomi Breslau of Henry Ford Health System in Detroit.

"There is reason to worry about these findings," Breslau says. "Nicotine dependence makes it much harder for a person to quit smoking cigarettes."

Her investigation, published in the September ARCHIVES OF GENERAL PSYCHIATRY and based on data collected in 1992, provides the first national data on nicotine-dependence rates. Other studies, such as the annual Monitoring the Future survey of drug use among U.S. teens and young adults, examine daily cigarette use but not nicotine dependence.

Since 1987, the American Psychiatric Association's manual of mental disorders has listed nicotine dependence as a form of drug dependence. Cardinal signs include an inability to control cigarette use, distress at not being able to quit, and harsh withdrawal symptoms in the absence of nicotine use.

Critics argue that this diagnosis wrongly treats a behavioral problem as a medical illness. But if the new findings hold up, they'll highlight the overlooked need for physicians to treat teenage nicotine dependence, remarks psychiatrist John R. Hughes of the University of Vermont in Burlington.

Breslau's group analyzed data on tobacco use and nicotine dependence for a national sample of 4,414 people, ages 15 to 54. This survey was part of a government-funded study of mental disorders.

Half the volunteers reported having smoked cigarettes every day for a month or more sometime in their lives. One in four smokers had become addicted at some point. Symptoms of this dependence usually didn't emerge until at least a year after daily cigarette use had begun, the researchers say.

Nicotine-dependence rates for daily smokers didn't vary between males and females or between those with little and lots of education. However, black cigarette smokers reported less nicotine dependence than their white counterparts.

The lowest incidence of daily cigarette use--reaching about 36 percent--occurred among 15- to 24-year-olds. This figure rose in successive age groups to a peak of 60 percent among 45- to 54-year-olds.

In contrast, daily smokers in the youngest age group exhibited a stronger tendency to become addicted than their older counterparts. For those young smokers whose daily cigarette use had lasted 6 years, for example, nicotine dependence rates hit 60 percent. Only 10 percent of the corresponding group of 45-to 54-year-olds had ever been addicted.

Breslau's team now will examine data for young people who have completed the same surveys since 1992. If the same results emerge, she says, scientists will need to expand efforts to identify biological and social factors that boost susceptibility to nicotine dependence.

A rise in nicotine dependence among young cigarette smokers wouldn't surprise Jerald G. Bachman of the University of Michigan in Ann Arbor. Cigarettes are among the most dependency-producing substances, says Bachman, a codirector of the Monitoring the Future surveys. Despite the overall downturn in the past 2 decades, he notes, rates of daily cigarette smoking by young people have risen slightly in the past few years.