On Wednesday, barring a last minute hitch, the District of Columbia will break ground for a massive convention center, drowning out with jackhammers a decade-old dispute over whether it's a good idea.

In the middle of a decaying part of downtown, where previously tourists visited with their collars turned up and their eyes cast down, a gathering place will spring up, soon to be followed by hotels, offices and stores expected to draw millions of dollars into an economy that needs them.

Official ceremonies are scheduled to start at 10 a.m., at 10th and H Streets NW, with Mayor Marion Barry and other city, business and labor leaders on the program.

With most of the land acquired and most of the site cleared, with a board chosen to oversee the center's operations, with streets closed off and construction workers poised to begin, the center seems certain to move inexorably ahead despite pending legal challenges from foes of the center.

And with that progress, arguments over its success shift from the hypothetical to the very real.

City officials apparently resolved any doubts they may have had in favor of the convention center long ago. Among those officials is Mayor Barry, who wasn't a clear convention center convert when he took office.

At this point, supporters of the complex are not likely to change the cheerful tune they've been singing about the convention center to the council, the Congress and the voters. That means, in the face of an apparent downturn in the economy, they have no fear.

It also means they don't anticipate tight credit will linger long enough to seriously slow hotel construction around the $98.7 million center, which will be built on a 9.7-acre site between 9th and 11th streets and H Street and New York Avenue.

It means they are ready to pitch in and sell the convention center in August when the annual convention of the American Society of Association Executives brings to the District government's doorstep probably the largest single group of people who make decisions about where conventions will be held.

The ASAE convention is one that all convention center salesmen attend, setting up booths and hawking their cities' attractions, hoping to snag meetings and conventions.

"It's very good timing to have us here when the hall is getting off of the ground," said James Lowe, president of the ASAE. Lowe said he expects Barry will be on hand to welcome about 5,000 delegates to Washington, and said the city will take advantage of the meeting to peddle its new center.

Almost without exception, people who stage conventions and use convention centers and directors of other convention centers call construction of the Washington center a good idea, long overdue. The center is scheduled to be completed in mid-1982.

"The fact that Washington has never had a building is just incredible," said Jeter Walker, director of the Norfolk convention and visitors bureau. "Every group in the country wants to go to Washington."

"In th U.S., every city has a convention center," said Lowe. "You can't compete without one." Lowe said his own group will have outgrown Washington's convention hotels after this year's meetings. A number of large hotels in the city, including the Sheraton Park, the Washington Hilton and the Shoreham-Americana, can handle large conventions, but supporters of the center have argued that the city loses the largest groups because it cannot accommodate them.

The city has also lost smaller conventions simply because the hotels cannot accommodate as many groups as want to come to the city at any given time. "We have bookings through the 1980s and the 1990s," said Penny Cummings, a spokeswoman for the Sheraton Park, which brought 375,000 convention delegates into the city in 1979. "We have tentative bookings almost up to the year 2000," she said.

"Washington has been, and is right now, a good convention center," said John Fondersmith, the city planning official who has overseen development of the convention center for years. "But we're still losing the market for 320,000 additional delegates a year because we haven't had suitable space."

In spite of optimism about the convention center and how it will fare, the project still has its critics. Challenges remain to the center, including possible delays over the demolition of historic buildings on the site. The buildings -- the beaux arts Elks Lodge Building at 9th and H streets NW, the American Mosaic building on I Street and the Mt. Vernon Theater on 9th -- are still standing, pending a determination on whether their historic value overrides the importance of the convention center.

Opponents of the center are not reconciled to its construction, said Carol Currie Gidley, a D.C. resident and activist. Instead, they are "terrified because we don't have enough money in the city to keep basic services going," she said, alluding to the city's multimillion-dollar deficit. "If we could get rid of this thing, it would help."

Barry "is intent on breaking ground in time even if we don't have the money to do it," she said. Gidley said she was struck by the irony of a government laying off workers to save money and at the same time pumping millions of dollars into a convention center on the still unproven theory that it will help cure the city's unemployment problem.

In fact, city officials are proud of the fact that the groundbreaking will move forward on the date promised more than a year ago. They hope adhering to a timetable will help allay skepticism about the convention center that grew during the years when it was an on-again, off-again project.

Once the center is up, the city is convinced that the development of hotels, office space and retail stores will occur that will make the area around the center a vibrant, productive part of the city.

"We are certainly confident that it's going to happen," Fondersmith said. "We're going to get a very sizeable mass of development, some very close to the center and some spread around.

"Even if this market situation hadn't happened, we really wouldn't have expected everybody would roll out and start developing the day after ground breaking," he said. But Fondersmith said he expected any delay in spin-off development because of tight money and high interest rates to be shortlived.

The city's zoning commission will consider creating a downtown hotel incentive zone to the east of the convention center site that might stimulate development in the area. Such a plan probably would allow developers to build slightly larger buildings than the area is otherwise zoned for.

In fact, the city already credits the convention center with creating spin-off development worth $45 million a year in revenue to the city. However, the city's reports, prepared under a congressional requirement, include developments that the city concedes are not solely attributable to the convention center.

For instance, one of the projects listed, like the Dolley Madison Hotel itself, is not designed to serve the major convention market directly, but rather is "intended to provide a refined and personal level of service to a distinguished clientele," wrote Madison Hotel president Marshall Coyne in 1978. "At the same time . . . we recognize that a convention center would bring major benefits to the District . . . as a whole . . . It is the prospect of this spreading renaissance of the area that helped influence my decision to invest," he wrote. r

"Developers are not only looking at the convention center, but other things that are coming together," Fondersmith said. He said he expects the Pennsylvania Avenue Development area to act as a bridge from the monumental part of Washington to the area around the convention center and to the fast-developing retail core near Metro Center. "It fits in with the mayor's plan for a living downtown."

The $21.4 million site acquisition costs were paid for by special taxes, including a tax of 80 cents per night on hotel room rentals and a 10 percent surtax on the business franchise tax, half of which is used for the convention center.

Construction costs are expected to be financed through long-term borrowing once the city goes to the bond market. When the center is in full operation in fiscal 1985, the estimated annual cost to the city will be $7.1 million, including $6.6 million needed annually to repay the money borrowed for construction and the half million dollars a year the center is expected to lose in its operations.

Like virtually every other convention center in the country, the D.C. center is expected to lose money in its operations but to more than make up the loss through money spent by convention delegates.

Another major hope pinned on the convention center is that it will generate decent jobs for District residents.

"We're not trying to create another K Street," said David Smith, of the city's economic development office. In that area, the "three A's -- attorneys, accountants and associations" provide jobs mainly for people who live outside the city, he said.

"Approximately 80 percent of the employes of hotels are District residents, and the wages are good," he said. "Putting people to work in hotels should not be considered to be some kind of sweat shop."

"The pieces are coming together" that spell the renaissance of downtown Washington, Fondersmith said. As important as the center will be in terms of development and jobs, he said, it also has another value.

"It's important in a very symbolic sense," Fondersmith said. "You don't have to go back too far, just to the early 1960s, to a point where some people saw the center city going down the tubes."

The city fought hard to keep that from happening and the convention center will be a symbol of that success, he said.