The D.C. Public Service Commission has initiated a detailed study that could lead to the first major changes in at least half a century for Washington's sometimes controversial taxicab zone boundaries.

Aided by a $55,250 grant from the U.S. Department of Transportation, the PSC will join with two other District of Columbia agencies in hiring a consultant to see what is wrong -- and what is right -- with the zone system.

Armed with the information, the PSC is expected to decide next spring whether to redraw the boundary lines of the four major zones and numerous subzones used for calculating fares.

The PSC agreed last October to consider the zone changes when it granted a 13 percent average increase in cab fares. Much of the time since then has been devoted to sparring at informal meetings attended by various factions of the city's splintered cab industry.

Unlike most cities, where drivers are on company payrolls, most Washington hackers own their own cabs or rent them from fleet operators. They pay their own expenses of driving and keep as profit what is left over from fare collections.

Washington uses a zone system because Congress in the early 1930s forbade the city from adopting the meters used in most other cities. Earlier this week, the prohibition was renewed by the House of Representatives when it routinely included the meter ban in its bill approving the D.C. budget for the 1981 fiscal year.

On the zone map that has been used for decades, Zone 1 has lumped together Capitol Hill and the entire downtown area -- a scheme that gives members of Congress and their staffers a cheap ride downtown and lobbyists an equally cheap ride to the Capitol.

A cab rider can now pay a one-zone fare of $1.45 to travel from the backdoor of the Library of Congress, two blocks east of the Capitol, almost to the Washington Hilton Hotel -- a distance of three miles through the congested downtown area. But another passenger pays a two-zone fare of $2.15 to ride just six blocks from the Library of Congress to Eastern Market. (In the evening rush hour, both trips would cost 65 cents more.)

A trip from downtown to the outer edges of the city -- for example, Chevy Chase Circle -- costs $3.55.

Despite the meter ban, the PSC has full power to redraw the zone boundaries as well as to set the level of fares.

It is likely to hold public hearings before making any changes. Cab organizations generally have proposed that the zone line be redrawn to put Capitol Hill outside Zone 1. One problem is whether nearby Union Station, an increasingly popular pickup point for cab riders as a result of the resurgence of rail travel, should be included within a redrawn downtown zone or the Capitol Hill zone.

Melvin E. Washington, general counsel of the PSC, said the PSC will be joined in overseeing the study by the D.C. Department of Transportation and by the Office of the People's Counsel, which represents the general public's interests in PSC proceedings.

Washington said a consultant soon to be hired, but not yet chosen, will explore such areas as riding patterns, travel times, operating costs and the competitive problems created by the opening and expansion of the Metro subway. He said information collected by the consultant will be available to all participants in hearings prior to next year's decision.

Many drivers contend the subway has skimmed off much of their former patronage, and some have voiced fears that higher cab fares would lose still more of their riders. A subway trip from downtown to the Capitol South station costs 50 cents in offpeak hours, approximately one-third of the $1.45 cab fare.

In a related development, one cab industry organization, the Taxicab Industry Group, applied to the PSC last week for a 20-percent increase in current cab fares.