A month ago I wrote that the Civil Aeronautics Board was just about at the end of its rope on the question of smoking regulations aboard airplanes.

Last month, it set in motion a plan that CAB aides believe will end up turning the whole matter over to the airlines. The plan is laid out in the Dec. 18 Federal Register (page 83206) as background to a new rule that permits any airline to go to the CAB and seek a waiver allowing it to replace the federal rule with any one the applicant wants to try.

The board's present rule required scheduled and charter airlines to maintain at least two rows of seats in each class of service for nonsmokers, expandable to accommodate all passengers who want to sit there.In addition, there is to be a special section for cigar and pipe smokers.

Since May 1979, however, the board has received other proposals, including a section for people who are unusually susceptible to smoke, such as asthmatics; a "buffer" section between smokers and nonsmokers; a ban on pipe smoking and cigars; a ban on all smoking on short flights and small planes, and a waiver to allow the airlines to set their own rules.

Not surprisingly, the CAB has approved only the waiver idea. At the same time, it scheduled oral argument on the proposals that either all smoking be banned or all rules governing smoking be revoked to allow each carrier to establish its own policy.

The register notice said the waiver "will permit experimentation and encourage innovation by the airlines," but so far, apparently, no airline has asked for one.

The CAB also plans to use the interest in waivers to provide, as the register notice says, "an indication of the effect of lessened government regulation in this area" to aid in deciding whether the smoking rule "needs to be transferred to another government agency after our sunset."

That's a vivid reminder that the CAB is scheduled to go out of business in 1985.