THE REGION; On Shrinking The Subways

One way to save New York's subway system, some transit planners have been suggesting, is to do away with part of it. Last week, under prodding from City Councilwoman Carol Greitzer of Manhattan, the Transit Authority acknowledged that it would formally study the possibility of eliminating parts of 11 lines.

The sections - parts of the No. 1, 2, 4 and 5 lines, the A, F, GG, J, M, and N trains and the Franklin Avenue shuttle - are predominantly in poor neighborhoods in Brooklyn, Queens and the Bronx. They have been described as suffering from declining ridership and a need for expensive rebuilding. Moreover, duplicate service from a subway or bus line is often available nearby, according to previous studies by the authority. The segments include 79 stations and 45 miles of track, or 6.5 percent of the 710-mile system.

''It's premature for anyone to worry about lines closing,'' said John Cunningham, a spokesman for the authority. The study, he said, would be undertaken to determine if cuts in service were necessary.

But Councilwoman Greitzer, among others, called the idea of planned shrinkage ''an outrage.'' ''One of the greatest assets of the system is the routes that exist,'' she said. ''We should not scuttle them.'' An official of the Straphangers Campaign, a riders group, contended that the Transit Authority often undercounted riders in poor neighborhoods, although she conceded that was in part because of failure to account for turnstile jumpers.

The Regional Plan Association and others have contended that the subway system should be trimmed in certain areas and expanded in others to follow population shifts.