During Prohibition, making and selling liquor was illegal, but drinking it was not. With tobacco, we are moving toward the opposite situation, where it will be legal to make and sell cigarettes but not to smoke them.

A smoking ban recently approved by the city council of Belmont, Calif., a town halfway between San Jose and San Francisco, is so sweeping that saying where it does not apply is easier than saying where it does. Smoking will still be allowed in tobacco shops, in automobiles, in some hotel rooms, in private residences that do not share a floor or ceiling with other private residences, and on streets and sidewalks, assuming you can find a spot that is not within 20 feet of a smoke-free location.

That may be hard, since Belmont's smoke-free areas include not only buildings open to the public but outdoor locations where people wait, such as ATM lines and bus stops, or work, such as construction sites and restaurant patios. But a smoker who despairs of finding an outdoor area where smoking is allowed can still light up even if he does not own a car and is unlucky enough to live in an apartment or condominium. He just has to land a role in a theatrical production "where smoking is an integral part of the story."

Meanwhile, the Los Angeles suburb that dubbed itself "Clean Air Calabasas" when it was leading the smoke-free march into the great outdoors is considering an extension of its ordinance that would cover apartments. Even if your landlord doesn't care whether you smoke, Clean Air Calabasas does.

The official justification for these ever-more-intrusive smoking bans is that the slightest whiff of secondhand smoke poses an intolerable hazard. The Belmont ordinance claims tobacco smoke is "extremely dangerous," regardless of dose, and warns that even "exposure to outdoor secondhand smoke may present a hazard under certain conditions of wind and smoker proximity."

Predictably, the ordinance cites former Surgeon General Richard Carmona's assertion that "there is no risk-free level of secondhand smoke exposure." But this pseudoscientific leap of faith amounts to saying that every little bit hurts, even if the damage can't be measured.

Epidemiological studies generally find that adults who live with smokers for decades are slightly more likely to get lung cancer and heart disease. The difference is so small that it's hard to say whether it signifies a causal relationship. There is also evidence that very young children of smokers are more prone to earaches and lower respiratory infections.

What do these studies of prolonged, relatively intense exposure prove about a little smoke seeping under the door of your apartment or wafting your way on the street? Absolutely nothing.

But the politicians who take the misleading statements of public-health officials like Carmona and run with them cannot be bothered by the facts. New York Assemblywoman Sandra Galef (D-Ossining), who wants to ban smoking on playgrounds, recently told Newsday that "the scientific reports say that secondhand smoke has as much of a negative effect on your health as smoking directly."

Got that, kids? If your parents smoke, you might as well start smoking yourself; the health effects won't be any worse.

One of Galef's colleagues, Assemblyman Ivan Lafayette (D-Queens), said lighting up around children is worse than physical abuse. "They're both horrible things," Lafayette averred, "but one is going to kill the child."

As those remarks suggest, the next rationale for banning smoking in private residences may be child protection, which will allow the government to go after smokers in detached homes as well as apartments. Already several state and local jurisdictions have banned smoking in cars carrying minors.

Such laws raise the question of why legislators are ignoring the setting in which the vast majority of children's exposure to secondhand smoke occurs. Now that anti-smoking crusaders have crossed the threshold into people's homes, they are not likely to turn back.