The District of Columbia Public Service Commission yesterday ordered the first study in 16 years of possible revisions in the District's complicated taxicab zone fare system.

The study could lead to extensive revision of the fare zones, which taxi drivers and riders alike have condemned as unfair and inconsistent.

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 passengers in other neighborhoods can travel for 20 minutes and several miles on a two-zone fare for $2.15.

The Public Service Commission was asked by the taxi industry a year and a half ago to redraw the zone fare map, but put off the controversial issue while it decided a basic taxi fare increase.

Two fare increases have been granted and now the agency will start a two-phase study of the zone fare system, according to Malvin Doxie, the PSC's staff director.

First the commission will look at the present zone map to decide whether it is "fair, just and nondiscriminatory." Riders and drivers will be asked to document and detail their gripes about fares that seem to be out of proportion to the length of the trip. Then the PSC will tackle the task of redrawing the fare zone map, or developing an alternative.

One alternative to the present zones, a taxi industry source said, might be a grid system that would more directly link fares to the distance traveled.

The commission has been blocked by Congress from ordering District of Columbia cabs to install meters like those used in virtually every other major city in the country. A rider tacked every year onto the District's appropriation bill prohibits the city from spending any funds on a study of meters. Without a study, the PSC would have no legal basis for putting in meters.

Doxie said the D.C. people's counsel, which represents the public interest in commission matters, hopes to get a grant from the U.S. Department of Transportation to study changes in the fare system.

Public hearings will be held before any new zone fare system is adopted and the controversy could also bring action from Capital Hill. Congress has long been blamed for some of the inequities in the present zone system, which has been in effect since 1964.

One of the taxi drivers' biggest beefs -- and one of the biggest bargains for riders -- is the trip from Capitol Hill to Northwest Washington, where many members of Congress and congressional staff members live.

From the Capitol to the intersection of Wisconsin Avenue and Calvert Street -- a trip that covers several miles and can take 20 minutes or more, the fare is for two zones, $2.15 under current fares.

On the other hand, the ride from Providence Hospital in Northeast Washington to downtown, a five-minute ride under most traffic conditions, crosses three zones and costs $2.85.

A trip from Benning Road NE down East Capitol Street to downtown normally takes six or seven minutes, but is a four-zone ride, costing $3.55.

The commission is expected to study the daily trip records of hundreds of cabs and thousands of trips in an effort to answer several questions about the fare zones, such as: What is the geographic pattern of taxi travel within the zone boundaries? How long is the average waiting time for a cab at various points in the city? Do riders on trips from some zones subsidize passengers in other zones?

To finance the studies, the commission ordered that District cab drivers pay a special $10 assessment the next time they renew their licenses.