The District is moving ahead with a detailed study and initial engineering for a transportation complex near the new convention center that could include 7,200 parking spaces and connections to buses, the subway and a planned downtown trolley service.

The underground center, proposed for six city blocks between New York and Massachusetts avenues NW near Mount Vernon Square, would be designed to draw visitors and commuters entering the city primarily on Interstate 395 and to keep them from crowding their cars onto downtown streets.

D.C. officials, who described the initiative last week, said they hope to entice private investors into developing a major entertainment complex above the depot, perhaps including movie theaters, restaurants and a new opera house. An entertainment complex could further enhance the attraction of an area already home to MCI Center and the under-construction convention center, while reducing the public cost for a project whose price tag could approach $300 million.

"It's hard to envision this, because of its cost, without some private development," said Deborah A. Price, transportation director in the D.C. Public Works Department.

The property identified for the transportation hub is situated between the entrance to I-395 and the vast muddy hole where the new convention center will rise. The 17-acre expanse is now home to several rudimentary parking lots, auto repair shops and modest stores, interspersed with a few blighted brick buildings and weedy vacant tracts. The site also includes the Museum Square Apartments, the Immigration and Naturalization Service building and the House of Ruth, a group home for women.

An initial review, completed last month, recommended that the District proceed with a more detailed analysis of the proposal, and officials are preparing this summer to begin an environmental study and preliminary engineering, requiring at least a year. Transportation officials expect to cover the cost of the studies with $1.2 million in federal highway and transit funds already allocated to the District, Price said. Once that work is finished, D.C. officials will determine whether to move ahead with the project, which she said would be unique in the Washington area.

"This is an important project for the region. It eases the congestion on local streets and provides ease of movement for commuters," she said.

The center already has won a tentative endorsement from the Metropolitan Washington Council of Governments, whose Transportation Planning Board voted last month to include the project in its area-wide plan.

"From a regional perspective, it's exactly the kind of thing we're trying to encourage," said John Mason, vice chairman of the transportation panel and mayor of Fairfax City. "It's very important to try to reduce the internal circulation of automobiles."

The initial study, conducted by a team of consultants headed by KPMG Peat Marwick, considered two options for the center. The first option would have 7,200 parking spaces and would cost $289 million. A more modest design would have 2,000 spaces and would cost $75 million. Price cautioned that those estimates do not reflect the entire expense of acquiring the tract, including the cost of buying out and relocating current property owners.

Though other sites could be considered, officials said the tract has several compelling advantages.

First, the location near I-395 makes it accessible to motorists from Virginia and to those from Maryland who drive to the city by taking the Baltimore-Washington Parkway or Route 50 to I-295 and the Southeast Freeway.

The initial study said the District would have to spend about $15.4 million to upgrade I-395 to accommodate the additional traffic. That does not include the previously proposed construction of a tunnel to connect I-395 and New York Avenue, estimated to cost $340 million to $600 million.

The site is also a quick walk from two Metrorail stops, Mount Vernon Square-UDC and Gallery Place-Chinatown, though Price said shuttles might be provided to ferry riders between the center and the stations. Also, Metrobus routes could be redesigned to run through the center, and tourist buses, which now clog downtown streets, would be directed toward the center to unload passengers.

With the district now envisioning the development of a trolley or light-rail line as part of its 20-year transportation plan, the center would be a natural stop on a proposed route that would run along M Street, Seventh Street and Georgia Avenue NW and serve both tourists and the downtown work force.

Proximity to the new convention center is also considered a plus. In fact, Price said, the transportation center also could serve as a depot for trucks supplying equipment and for conventions and exhibitions. The proposed site is also close to the proposed location of a baseball stadium in the Mount Vernon Square area, officials said.

Property owners in the area east of Mount Vernon Square have yet to learn the details of the District's proposal. When told of the specifics by a reporter, Christel Nichols, executive director of the House of Ruth, said she does not want her program evicted.

"It could be a very big deal for us to move," she said.