ASPURT IN the number of area jurisdictions considering bans on smoking in restaurants and bars may deflate one frequent objection: that businesses would lose customers to neighboring jurisdictions. Last week, Howard County, which since 1996 has banned smoking in restaurants and bars unless they have separately ventilated smoking rooms, became the fourth area jurisdiction to consider a total prohibition. County Executive James N. Robey's proposal is similar to legislation passed in Montgomery County in 2003 and is being considered in Prince George's County and the District. As reported by The Post's Amit R. Paley, if all these proposed bans take effect without delays or loopholes -- no sure thing, but support has been picking up -- the area could wind up with a smoke-free zone stretching from the White House almost to Baltimore.

Just how far from their local pubs and eateries will smokers go to wine and dine in a carcinogenic confine? The more contiguous jurisdictions that approve bans, the less likely that no-smoking spots will suffer desertions. So expand that zone, save the businesses and strike a blow for public health. What about entire states? Supporters of the bans say momentum is building in Annapolis for a statewide law, but support has come up just short in the past. In Richmond, where King Tobacco has yet to abdicate, prospects are dim.

As it happens, the claims of lost business don't seem to wash anyway. A report released Tuesday by the Montgomery County Council showed that the county's smoking ban has had no significant effect on restaurant revenue and employment. Some opponents argued that the report was not reliable because it was commissioned by supporters of the ban. But the report is thorough; it compares the county's revenue and employment figures to those of with similar jurisdictions without bans.

Policymakers in this area and elsewhere are realizing that allowing poisonous air to permeate public gathering places jeopardizes the health of workers as well as customers. Just as restaurants are required to serve safe food, they should have to provide safe air. Howard, Prince George's and the District should move to make this as clear as that air ought to be.