On the city map, the proposed convention center site is a small puzzle piece that fits neatly into the city's plans for redeveloping a decaying part of the old downtown area.

Whether it falls into place is up to the Congress, which must decide whether to allow the city to borrow $27.7 million from the federal treasury to start buying 9.7 acres of land - three blocks and a scrap of park just southwest of Mt. Vernon Square - and designing the facility. The rest of the financing would be done in the same way at high interest rates.

The city and the business community, in support of the $110 million project, have produced huge studies, promising estimates of anticipated revenue and jobs, support from the nearby Chinese community and vows by major associations to take their convention business elsewhere until the city builds a new facility. On the other side of the scales skeptics have weighted in with questions about use and revenue estimates, competition from hotels and other existing facilities and other "what ifs . . ."

Preliminary designs for the convention center include a 300,000 square foot exhibition hall large enough to accommodate major conventions, including the political conventions, the trade shows, with seating for 30,000 persons. The building would also include 40 meeting rooms.Several hotels have indicated that they will build near the center if it is constructed.

"I support any project that would revitalize the downtown area of D.C.," said Sen. Patrick J. Leahy (D-Vt.), chairman of the Senate District Appropriations Subcommittee. "But I'm still concerned about the proposed civic center."

Leahy, who has walked the area twice, said he is concerned that there may be "significant relocation problems for many of the homes and businesses in the area." Some may be happy to sell, but others "have expressed fear that they won't be able to relocate elsewhere," he said.

City planners, with maps and charts and graphs in hand, say there is a convincing case for where they plan to put the convention center, putting it into perspective surrounded by other redevelopment projects. The site was chosen from among 13 others, in part for its closeness to Metro and its nearness to the downtown retail area and major tourist attractions such as the White House and Capitol.

North of the proposed site are Mt. Vernon Square and the planned downtown campus of the University of the District of Columbia. To the south are the Martin Luther King Jr. Library, two national art galleries, two subway stops, department stores and Pennsylvania Avenue, where large-scale commercial and residential redevelopment are planned.

Chinatown, proposed housing on the Wax Museum site and the new Hyatt-Regency hotel northwest of the Capitol are off to the east, and to the west are major office buildings.

Drop the convention center into the middle of the picture, say some proponents of the convention center, and the redevelopment of downtown is almost complete.

But the handful of blocks the convention center would replace is in a different world from the neatly plotted city of urban planners' maps. It is a city not found in architects' renderings and models, but the product of time, wine, no money and decay.

There is a stench in the air - stale beer, stale cigarette smoke and rotting garbage, mixed in the cloud of auto exhaust that chokes the city on hot summer days.

It is the kind of area most people walk around when they are on foot. Those who drive in lock their car doors. The 1968 riots hurt - not the burning and looting, which started just north of the neighborhood - but the aftermath. Many of those who could afford to be afraid deserted it.

Going door to door a visitor is heralded by the sound of buzzers, letting him past locked doors. As he leaves, he is followed by the sound of double locks, clicking shut. Much of the crime, however, is directed at the alcoholics who hang out in Mt. Vernon Square and nearby, according to a police officer who works in the area.

There is wreckage on the streets, staggering men and mumbling women. But there are others in the neighborhood, too - helpful, friendly men and women who live and work there, whose lives may soon be altered if the convention center is approved.

Generally, the attitude of those who stand to be most affected by the proposed convention center is that it would be an improvement in the neighborhood. But in addition there is fear about finding a new location and concern about individual welfare as well as skepticism about the project itself.