A new Harvard study claims that the tobacco industry in recent years has manipulated menthol levels in cigarettes to hook youngsters and maintain loyalty among smoking adults. The report could further inflame a controversy over menthol in pending tobacco legislation.

The study by researchers at the Harvard School of Public Health, released Wednesday, concludes that manufacturers have marketed brands to what it called a "vulnerable population" of adolescents and young adults by "manipulating sensory elements of cigarettes to promote initiation and dependence."

Young people, the study said, tolerate menthol cigarettes better than harsher nonmenthol cigarettes. In low-level menthol cigarettes, the menthol primarily masks harshness, making it easier to begin smoking. But as smokers become more accustomed to menthol, they prefer stronger menthol sensations, according to the study.

"Tobacco companies researched how controlling menthol levels could increase brand sales among specific groups," the study said.

"They discovered that products with higher menthol levels and stronger perceived menthol sensations suited long-term smokers of menthol cigarettes, and milder brands with lower menthol levels appealed to younger smokers."

The study concludes that 44 percent of smokers age 12 to 17 prefer menthol cigarettes, and it urges regulation of the tobacco industry and menthol, in particular.

Menthol cigarettes currently make up about 28 percent of the $70 billion cigarette industry in America.

A spokesman for the company that owns Philip Morris, whose Marlboro menthol brands are among those cited in the study, Wednesday denied that it has adjusted menthol levels as a way to lure young smokers.

But the study contends that Philip Morris employed a two-pronged strategy to compete better in the menthol market, a segment of its business that had been lagging before 2000.

The company introduced a new low-level menthol brand, Marlboro Milds, to compete with cigarettes like Newport, which contains a low level of menthol. At the same time, the study concluded, Philip Morris raised the menthol level in its Marlboro Menthol brand by 25 percent to appeal to adult smokers.

Since then, Philip Morris' share of the menthol market has increased, and it is currently the second-largest seller of menthol cigarettes in the United States.

A bill currently pending in Congress would give the Food and Drug Administration the authority to regulate tobacco products and remove cigarette additives, including menthol. But while the legislation would immediately ban many other flavorings, it specifically exempts menthol from such a ban.