BOSTON, JAN. 6 -- Doubling the nicotine in chewing gum prescribed to help people quit smoking sharply increases the likelihood that hard-core smokers using the gum will be able to kick the habit, Danish researchers reported today.

In a study published in the New England Journal of Medicine, researchers at Gentofte Hospital in Copenhagen found that nicotine gum containing 4 milligrams of nicotine enabled 33 percent of heavily addicted smokers to remain smokeless for at least two years.

Of the heavily dependent smokers in the study who used gum containing only 2 milligrams of nicotine, the amount in gum available in the United States, only 6 percent remained off cigarettes for two years.

Based on the findings, the researchers recommended that 4-milligram nicotine chewing gum be made available for heavily dependent cigarette smokers, even if it increased the risk that they may become hooked on the gum instead.

"What is the alternative?" said Dr. Philip Tonnesen, a pulmonary disease expert who headed the study. "If a patient does not use 4-milligram gum then maybe he will smoke 20 cigarettes a day."

In the study, 15 percent of the abstainers still were using nicotine gum after two years.

Karen Monaco of the American Lung Association said that more study probably would be needed to confirm the findings but that anything that can help people quit smoking would be wel- come.

A spokesman for Lakeside Pharmaceuticals of Cincinnati, Ohio, which makes Nicorette, the only nicotine gum approved for prescription use in the United States, said the company plans to apply for government approval to sell 4-milligram gum later this year.