AFTER 16 YEARS and countless toyings with a cab-fare schedule based on a twilight zone map, there's going to be an official look taken at how taxi charges are computed in the District. This nasty but necessary job will be undertaken by the D.C. Public Service Commission, which will study everything from map revisions to distance charts, time trials and maybe even the weather. Whatever comes of it surely can't be worse that the antiquated, complicated schedule now in use.

Under the present zone system, riders in some areas of the city must pay $2.85 for a three-zone trip that takes five minutes, while others in different neighborhoods can travel for 30 minutes and a batch of miles through two zones for $2.15. Similarly, drivers trying to make the best of it find themselves crusing between a rock and a hard place. Some what a meter system that would factor in time and mileage, but other vigorously oppose such a requirement as too expensive.

The commission plans to look first at the zone map to decide whether it is "fair, just and non-discriminatory." It is none of the above. Then -- and here comes the wild part -- riders and drivers will be invited to document their gripes about fares. (Perhaps we should pause right here while you recite your personal pet peeves.)

Newcomers may not know it, but all of us have Congress to thank for the system now in place, which just happens to include a fat zone running from Capitol Hill through a swath of downtown and Northwest where many of the lawmakers do most of their traveling. Not only did Congress think up this clever system, but it has forbidden even a study of meters.

Meters may not be the answer, but some fairer connection between distances and fares, through a grid map, would be an improvement. Any significant changes in the fare schedule that assist drivers should be accompanied by rules aimed at curbing poor service. Too much of the response to passengers' needs for transportation has been anything but " fair, just and non-discriminatory." More compensation is in order for the drivers. But there should be better recourse, too, for those who wave in vain.