Non-smokers traveling long distances on airplanes are probably inhaling as much smoke - possibly more - in the non-smoking sections as in the seats reserved for smokers, according to a new study by the National Cancer Institute.

Since last April, smoking has been banned on all U.S. domestic flights of two hours or less, but that ban is subject to congressional review in 1990. Meanwhile, longer flights on most airlines continue to have smoking in designated areas of the planes.

The study, published in last week's Journal of the American Medical Association, measured nicotine levels in the air in various cabin areas during four flights of four hours' duration.

It also measured levels of cotinine, a nicotine-related chemical, in the urine of five passengers and four flight attendants who traveled on all four flights over a 19-day period last May. The urine tests showed measurable traces of nicotine in their bodies up to three days after flying.

All participants were non-smokers. They wore monitors to measure nicotine in the air during the flights and for the 72 hours before and after traveling. Some traveled in smoking sections, some in non-smoking, but near smoking sections. Flight attendants were assigned to either section.

Everyone in the group also noted whether they had dry and burning eyes, coughing, sneezing, scratchy throats and headaches before, during and after their flights. An observer recorded hourly how many passengers were smoking. There was a maximum of eight people smoking at any one time on the monitored flights - possibly a lower rate than on some flights, the report noted.

"Measurable exposure to environmental tobacco smoke occurred for all subjects on all four flights," wrote the National Cancer Institute's Margaret Mattson.