There's only one thing wrong with the deal the District of Columbia has made to give developer Giuseppe Cecchi special incentives to build a high-technology exhibit center called Techworld:

Techworld doesn't have to be a high-tech exhibit center.

Nothing in the agreement with the city prevents Cecchi from turning Techworld into an ordinary office complex if his planned technology mart doesn't pan out.

Techworld has to be built according to the plans Cecchi has presented to the D.C. Zoning Commission, but apparently that is as far as the city's control over the project reaches.

The zoning commission's tentative approval of Techworld by a 3-2 vote two weeks ago was one of the most controversial decisions the panel has made in years. Techworld was endorsed enthusiastically by Mayor Marion Barry as a job-creator and criticized just as vehemently by planners and preservationists for messing up the city's historic plan.

Critics complained that the project is a blockbuster megaplex, too big for its neighborhood. Worse it will violate the city plan by destroying the vista down 8th Street NW between the Carnegie Library and the National Portrait Gallery three blocks away. Defenders cited the jobs Techworld would create; "It will provide personal opportunities for generations to come," said zoning board Chairwoman Maybelle T. Bennett.

Budgeted to cost $240 million, Techworld will cover two city blocks East of the D.C. Convention Center. When completed four years from now, Techworld will include a 900-room Ramada Inn and more than 1 million square feet of space that is supposed to be used for displays and offices of high-tech companies.

Development of the two blocks as a market place for computer and communications products was the crucial justification for allowing Cecchi to put up a bigger building than zoning regulations would ordinarily allow.

As a permanent electronics mart -- similar to the D.C. Design Center in Southwest -- the project would create more jobs than a mere office building, argued International Developers Inc., the firm headed by Cecchi.

Because exhibit space works best with large contiguous floors, IDI persuaded the city it was necessary to build a five-story high bridge across 8th Street NW linking buildings in the complex. The developer, however, has yet to promise the city that those five linked floors will be used exclusively for exhibit space.

At the urging of the developers, the city has also raised the height limit on the complex, approved the controversial bridge and agreed to close 8th street to traffic and shrink its width from 100 feet to as little as 60.

Squeezed in by 110-foot tall buildings and held down by a five-story bridge, the view up 8th Street envisioned by Charles Pierre L'Enfant will make the restored Carnegie Library look like "a billboard at the end of a tunnel," warned John Parsons, who represents the National Park Service on the zoning panel.

Architect of the Capitol George White -- who voted with Parsons to scale down the project and ban the bridge -- was even more skeptical. "You put a man on the moon, you ought to be able to sell high-tech products without putting a bridge over 8th Street," he said.

Esthetics lost to jobs on the vote, which zoning commission staff members describe as a "tentative preliminary action." The final vote will probably come in June after the commission staff and Cecchi's lawyers formalize the documents for what is known in zoning jargon as a Planned Unit Development or PUD.

That means there is still time for the city to insist that Cecchi guarantee that Techworld will be used as a tech mart to maximize the job gains and justify the special favors that come with the PUD designation. If Techworld is going to turn out to be little more than an office complex, there's no reason why it should receive special favors.

The question of whether they city might get less than it bargained for came up at least once during the 50 hours of hearings on Techworld. Zoning Commissioner Lindsley Williams asked whether Cecchi would have to tear down the bridge over 8th Street if the space were used for offices rather than exhibits.

The suggestion was treated as a joke.

But it is no more of a joke than approving the Techworld PUD without getting guarantees that it will be used as promised.

Demanding such guarantees is neither an abstract exercize nor a challenge to the developer's word. Cecchi's word is as good as his buildings and he has built Watergate, Monte Bello and the new Porto Vecchio project rising on the riverfront south of Alexandria.

But there is a not insignificant risk that Techworld will not make it as a high-tech merchandise mart. The nation's first such facility opened a couple of months ago in Dallas with half as many displays as expected. Yet two dozen more marts are being planned, suggesting the mart market may be both saturated and soft. Several rivals will open before Techworld debuts in 1989, starting with Boston's Boscom. It has already been scaled down as was the Dallas Infomart, which opened with about 100 permanent displays and is now projected to reach 200 rather than the earlier goal of 350.

The Dallas facility, however, has attracted far more trade shows and conventions than expected and that business may become crucial for Techworld.

The implicit reason why District economic development officials are so strongly behind Techworld is that it will greatly benefit the D.C. Convention Center. Techworld's groundfloor and lower level display space will vastly expand the facilities of the center, which simply isn't big enough for many trade shows. The permanent mart facilities and the moderately priced hotel at Techworld should also help draw more business to the Convention Center.

The Convention Center is already drawing development to the neighborhood and creating badly needed service jobs for the city. But the Center needs to continue growing, to attract both bigger events and more day in and day out business.

The synergy between Techworld and the Convention Center is the prize D.C. officials are seeking in their agressive campaign to win approval for the project, despite its serious shortcomings in architecture and urban planning.

If the District is going to sacrifice 200 years of city planning in the name of economic development, it should demand ironclad guarantees that Techworld will produce the promised benefits.