THE HOUSE of Representatives surprised everyone Monday night when it narrowly passed an amendment that would ban all smoking on airplane flights of two hours or less. Measures to curb in-air smoking have failed repeatedly; the now-defunct Civil Aeronautics Board barely missed passing one in 1984. Since then, though, public antismoking sentiment has soared, and so has evidence of danger to nonsokers from "sidestream" or "secondhand" smoke. It is concern over this passive hazard that has spurred the increased interest in banishing smoking altogether -- not just to smoking sections -- in office buildings, restaurants and other public places.

Airplanes are a more urgent case than any of these: they typically recycle their air supply, spreading cigarette smoke evenly among smoking and nonsmoking sections, and their flight attendants are obliged to breathe that air for long periods. The two-hour limit, a sensible compromise from an earlier proposal to ban in-air smoking altogether, would clear the air from 80 percent of all domestic flights while keeping smokers' discomfort to an acceptable minimum.

Fear of sidestream smoke, like antismoking sentiment in general, has the potential to become exaggerated and take on a tinge of zealotry, with a certain attendant callousness toward those hapless folks who can't quit. Rep. William Young of California, for instance, arguing in floor debate for a full smoking ban on all flights, suggested that if smokers are uncomfortable, "we can give them nicotine gum. We can give them nicotine liqueur. We can give them a cold tar sandwich." Triumphant supporters of the amendment said they had benefited by bringing forth "human" witnesses -- Rep. Mickey Leland testifying to his allergy to smoke, Rep. Donald Lukens describing his six operations for lung cancer -- while the opposition stressed procedure and the administrative burden on airports.

True, some details would have to be worked out (what happens on two-hour flights that get delayed to four hours?), but the hassle could be more than balanced by the gain in time at check-in counters where clerks no longer need to ask, "Smoking or non-smoking?" The burden argument usually comes from the tobacco interests, which will presumably give the measure a much rougher time in the Senate.

There is, of course, also a "human" argument against an all-flights ban, as there is against draconian smoking restrictions in general. Sympathy for their predicament suggests we not force behavior modification on confirmed addicts when intelligent halfway measures can do nearly as much to protect nearly everybody. The two-hour compromise is just such a measure, and deserves suppor