Recent studies indicate that exposure to cigarette smoke can increase the risk of cancer for a nonsmoker.

Estimates on the effect of cigarettes, pipes and cigars on passive smokers -- the two-thirds of the American population who don't smoke but are exposed to smoke by those who do -- range from 500 up to 5,000 extra cases of cancer each year. The highest estimate comes from a disputed study co-written this year by an Environmental Protection Agency epidemiologist. The Tobacco Institute said that studies claiming passive smoking causes cancer are based on "questionable research." "That has not been conclusively established as dangerous," said Jeff Ross, who advises businesses on employe smoking policies for the institute.

The Task Force on Environmental Cancer and Heart and Lung Disease recently devoted a conference workshop to the effect of passive smoking on the incidence of lung cancer.

"The panelists agreed that there probably is a link between passive smoking and lung cancer," said workshop Co-chairman Lawrence Garfinkel, vice president for epidemiology and statistics and director of cancer prevention at the American Cancer Society. He said that there are several published studies -- and more under way -- linking passive smoking to cancer. "Evidence is piling up" to prove that passive smokers have an increased risk of cancer, Garfinkel said. He also said studies have shown there are larger amounts of noxious chemicals in clouds of smoke from a cigarette than in the smoke that is inhaled.

The other head of the workshop, Lewis Kuller, chairman of the department of epidemiology of the University of Pittsburgh's School of Public Health, estimates that 1,500 lung cancers each year "could possibly be related to passive smoking." Kuller also fears that passive smoking contributes to heart attacks.

EPA epidimeologist James Repace has estimated that cigarette smoke can lead to between 500 and 5,000 deaths from lung cancer each year. He and co-researcher A. H. Lowrey, an epidemiologist for the Naval Research Laboratory in Washington, compared cancer rates in typical nonsmokers with those of Seventh Day Adventists, who are forbidden to smoke and who also tend not to have contact with smokers because they frequently marry and work with other Seventh Day Adventists, according to Repace and Lowrey.

Herman J. Gibb, an epidemiologist in the EPA's cancer assessment group, reviewed the report and criticized using Seventh Day Adventists as a control group, because they also do not drink and tend to pursue a more healthy life style than the general population. However, Gibb did support the report's lower estimate of 500 deaths per year attributed to passive smoking, which Repace and Lowry arrived at by using a different model.

The greatest difficulty in studying the effects of passive smoke is measuring the amount of exposure, researchers agree. Nonsmokers must compute their exposure to tobacco smoke by juggling the hours of exposure, amount of smoke, size of the work area and the ventilation system.

Kuller suggested that measuring the amount of cotinine in urine could allow a nonsmoker to judge his or her level of exposure. Because cotinine is produced in the body only by exposure to nicotine, a nonsmoker would be able to accurately judge the impact of passive smoking by measuring his or her cotinine level, he said.