It is permitted on the last 14 rows of Trailways buses but only on the last three rows of Greyhounds.

You can do it in most theaters if you are an actor or actress but not if your are merely watching.

Speaker Tip O'Neill is reputed to engage in it in the alcoves of the House floor, where it is allowed, and sometimes on the floor itself, where it is not.

You can do it in a restaurant in Minnesota, but only if that restaurant falls under the heading "bar" or "tavern."

Fifty-three million American adults do it, hardly any of them in elevators, and 34 million Americans, who are allergic or sensitive to it, presumably despise it.

"It" is the smoking of tobacco, and the 13-year-old controversy surrounding smoking and health has spawned a cottage industry of signs and placards, several hundred thousand signatures on a multitude of petitions and letters, an avalanche of legislation and regulatory action, and a good deal of name-calling.

The smoking controversy has been with Americans since the 1964 surgeon gerneral's report first linking cigarette smoking and disease. It used to be relatively simple. Smoking was bad for you but if you chose to do it, that was your problem.

Since 1972, however, things have gotten complicated. Five years ago the surgeon General reported a possible hazard to nonsmokers subjected to the fumes of their neighbors' habit. Suddenly smoking was everybody's problem.

In the old days tar and nicotine were the culprits, and smoke was smoke. Recent studies indicate, however, that the kind of smoke nonsmokers inhale, and that sidestream(non-smokers') smoke contains twice as much tar and nicotine and a host of harmful chemicals in alarming quantity. Carbon monoxide, for example, attains concentrations in smoke-filled rooms of twice the level recommended in federal safety guidelines. Exposure to such levels may result in impairment of visual and perceptual ability.

So say the health spokesmen and the manufacturers and wearers of button with slogans like "Stop Pulmonary Rape" and "Your Smoke, My Lungs." But either side can find plenty of sympathetic statistics, and studies cited by the R.J. Reynolds Tobacco Co., for example, support the conclusion that there is nothing conclusive on the subject.

Each side armed with statistics, the battle continues, and regulations increase, each signaling a barrage of name-calling by smoking interests.

"These groups are small organizations of petty tyrants gripped with a Carry nation mentality and they can't stand to see others enjoying themselves," says Bill Dwyer, a spokesman for the Tobacco Institute. "What these people want is prohibition with a capital "P"."

Two of the groups Dwyer, a smoker, refers to are ASH (Action on Smoking and Health) and GASP (Group Against Smokers' Pollution). While prohibition of the Carry Nation variety is a long way off - 688 billion cigarettes were manufactured in the United States last year - anti-smoking groups seem to be gaining ground with every new regulation.

Nationwide, more antismoking legislation has been passed in the past three years than in the previous 150, according to Clara Gouin, who founded the first GASP group in her College Park living room seven years ago. She said her father, a heavy smoker, had died of smoking-related diseases the year before.

Gouin, who "has friends who smoke but never in our home," is quietly determined. "We like to think that every nonsmoker is a potential GASPer."

Gouin has no idea how many GASPers are out there, members or potential members of around 80 chapters in the United States and Canada, but her mailing list numbers 5,000.

GASP and ASH work together closely and while their aims are similar to those of the American Lung Association, methods differ.

"The institutes do research and education and we go out and sue people," says John Banzhaf, head of ASH and reknowned veteran of smoking skirmishes, including the actions that got the Winchester man off the air in the late 1960s. (His "cigars" were rcled cigarettes in brown paper, and cigarette broadcast ads had been outlawed.)

Currently citizens' anti-smoking froups are engaged in actions with the Food and Srug Administration, the Civil Aeronautics board and the Federal Trade COmmission. The most controversial of these actions concern smoking in public.

Last week a proposed settlement was announced between Eastern Airlines and two nonsmokers' groups - ASH and the Ralph Nader-backed Aviation Porject - whereby the airline would pay $10,000 for frequently denying passenger requests to sit in nonsmoking sections. The airline also agreed to set aside an unprecedented number of nonsmoking seats.

If the CAB approves the settlement, Eastern must in the future set aside two-thirds of its shuttle flight seats and 60 to 65 per cent of its regular flight seats for nonsmokers.

The inflexible percentage is new idea, but, says Eastern spokeswoman June Farrell, "we've had that mix for a month - with zero reaction."

Farrell says she rode a shuttle recently and "the smokers puffed away in the back and everybody was happy - and, my gosh, a shuttle's only an hour long. You can have a cigarette before you get on and the second you get off, so it's not all that major ..."

Which is a good thing, since no one has yet figured out how to enforce nonsmoking regulations aboard aircraft, should the number of seats available for them and some nicotine-crazed addict cause a scene. "Disembark at the next scheduled stop" ha a handily ominous ring, but air shuttles stop only once.

A CAB proposal made public last October has inspired passionate responses on both sides. The CAB proposed to prohibit pipe and cigar smoking aboard commercial passenger aircraft and in addition solicited public comment on the idea of banning all smoking aboard planes.