Metro's old "Downtowner" minibuses could begin plying short-haul, localized routes in four District neighborhoods late this year, as part of a city program to expand public transportation in areas the city feels are underserved by Metrobus, according to acting D.C. Transit Director John Drayson.

There's a catch, however: Some Metrobus routes that now serve the four areas may later be curtailed, according to Drayson, because the city already is spending about $50 million on bus subsidies and would be hard pressed to come up with more.

But the cuts won't come immediately. The plan is to run the new routes alongside existing Metrobus service for six months and then to take stock of ridership and costs.

The city, meanwhile, would pay the full cost of subsidizing the new routes, tentatively estimated at $1 million, Drayson said. Eventually, Washington hopes to operate 12 such routes on its own.

City officials may organize a contest to select a special name for the new bus service, which would cater to people going shopping, heading for Metrorail stations or making other short trips. Current Metrobus service, city officials said, stresses longer trips to and from workplaces.

Narrow streets and sparse ridership have made Metro reluctant to route buses through some neighborhoods of the city.

Officials stress that details are subject to change. But currently under discussion are flat fares of 50 cents, with typical headways (time gaps between buses) of 15 minutes. Officials have settled tentatively on the following four routes and hope service will begin by year's end:

* Between L'Enfant Plaza Metrorail station, Waterside Mall and the intersection of Half and P streets SW. This route could bring changes in the existing Metrobus routes 70, V-4 and V-6.

* Between the Mayfair-Parkside area of Northeast and River Terrace. This route would pass the Minnesota Avenue Metro station and could alter the X-6 Metrobus.

* Between the Congress Heights neighborhood in Southeast and the Sears, Roebuck department store on Alabama Avenue. Drayson said this route was not likely to affect any existing Metrobus line.

* Between the Foggy Bottom Metro station in Northwest and the Safeway supermarket at 34th Street and Wisconsin Avenue in Georgetown. Metrobus routes 30, 32, 34, 36 and 38 could be affected by this service. The D.C. government currently spends about $300,000 annually subsidizing the 38 route (Ballston-Farragut Square), city officials said.

The buses would be 15 compact, 31-seat vehicles that plied the Downtowner routes until they were canceled in September as an economy measure. Though owned and operated by Metro, the buses probably would be financed wholly by the D.C. government, as the Downtowner service was. This arrangement would allow the city to establish fares and routes without having to obtain approval from the suburban governments that also are members of Metro.

During a two-week period in July, meetings were convened in six city neighborhoods to get citizen input for the bus scheme. Project manager John F. Donahue Jr., who attended the meetings, called public reaction "very positive," but noted that a few people expressed concern over possible cutbacks in existing Metrobus service.

The program calls for eight additional routes eventually to be added to the scheme as federal funds are obtained to purchase new buses.

Among those being considered: Fort Lincoln-Brookland; Fort Lincoln-Hechinger Mall; Southeast Community Hospital-Good Hope Road shopping district; Eastland Gardens-Ridge Road; Zoo Metro station-Brookland station; Dupont Circle-Washington Hospital Center; Good Hope Road shopping district-Benning Road Metro station; Capitol Heights-Deanwood station; Waterside Mall-Eastern Market; and Union Station-Potomac Avenue Metro station.