Developer Giuseppe Cecchi, his demands to change restrictive zoning conditions on the massive Techworld high-tech trade mart he plans to build next to the Washington Convention Center rebuffed, said yesterday that he will circumvent them by erecting a smaller facility under the existing zoning regulations.

Cecchi said he plans to break ground on the $220 million project on Oct. 15, open an 850-room Ramada Hotel and 60 percent of the trade center by late 1987, and complete the complex a year later.

The developer said that he could not accept some of the 36 conditions imposed by the D.C. Zoning Commission to grant approval for constructing a larger complex, particularly one that would permanently have limited the use of offices in the building to those that were related to the trade center.

Cecchi said lenders would have refused to finance the project with such a restriction. Last week the Zoning Commission rejected his demand that the offices just be "primarily" geared to the trade center and that the requirement apply only during an unspecified "initial lease period."

Cecchi, the developer of the Watergate complex, said that this week he decided to trim his planned 1,570,000-square-foot complex to the 1,400,000 square feet allowed under existing zoning provisions.

"I can assure you that this decision was not made lightly," he declared at a news conference at Techworld's construction headquarters on a corner of the virtually vacant two-block site bounded by Seventh, Ninth, I and K streets NW. "The bottom-line considerations for Techworld are its financability, its marketability and the stability of its economic results over an extended period of time.

"Unfortunately, the restrictive nature of some of the 36 conditions . . . and the associated controversy would have seriously jeopardized these bottom-line requirements and would have outweighed the advantage of the additional floor area."

Cecchi said later, "We are not bound anymore by the 36 conditions."

He said that as a result, his firm, International Developers Inc., will have "no problem in obtaining construction and permanent financing."

Among the conditions that Cecchi said he plans to ignore is one that would have cut the bottom floor off of his controversial six-story-high passageway between the two wings of the complex, starting 65 feet above Eighth Street NW.

The 55-year-old developer said that he plans to build the six-story bridge, which he has said is necessary to provide adequate space for displays of high-tech products. The bridge plan has drawn vehement protests from the Smithsonian Institution, the D.C. Preservation League and the Committee of 100 on the Federal City, an urban planning group.

The Smithsonian and the other groups have claimed that the bridge and Cecchi's plan to close Eighth Street, narrow it, and turn it into a walkway and courtyard for Techworld would ruin the street's vista as envisioned in Pierre L'Enfant's 1793 plan for the development of the nation's capital.

The Eighth Street view, now unobstructed, extends from the University of the District of Columbia's Carnegie Library on K Street south to the National Museum of American Art on G Street.

Maureen E. Mahoney, a lawyer for the preservation group and the Committee of 100, said the groups "have always taken the view that he would not be able to build the bridge over Eighth Street as a matter of right." But she said the groups have not decided what further action they might take to try to prevent its construction.

Mahoney said that Cecchi "told the commission he needed that extra 170,000 square feet of space for a trade mart. Now he says he doesn't. What's that to lead us to believe about the other representations he's made, such as the necessity of the bridge?"

She noted that a D.C. City Council committee, when it approved the Eighth Street closing and construction of the bridge, stated that if the Zoning Commission made the conditions more restrictive, they would take precedence over the council's.

"The whole understanding was that he would check in with the Zoning Commission and that the Zoning Commission will have the last word," Mahoney said. "Cecchi is trying to circumvent the council's intent."

None of the five zoning commissioners could be reached for comment yesterday. Steven E. Sher, the commission's executive director, said the commission "cannot prevent matter-of-right zoning" but that it "could prevent his withdrawal" of the proposal for the larger project.

"It's unclear what would happen then," Sher said.

The commission canceled its meeting for next Tuesday, which had been scheduled to discuss further Cecchi's demands for revisions of the 36 conditions it had imposed. Sher said the commission will discuss the case again at its Sept. 9 meeting.

The commission approved the larger project on a 3-to-2 vote last March. But several commissioners voiced their anger and irritation last week at Cecchi's demands for further concessions.

Commissioner Lindsley Williams voted for Techworld but said the commission was "not going to write in all manner of flexibility." He nonetheless voiced the fear that by rejecting Cecchi's demands, the city would end up with "a crummy matter-of-right" development.

Other city officials, including Mayor Marion Barry, long have supported Cecchi's plans as the keystone to redevelopment of the faded blocks surrounding the 2 1/2-year-old Convention Center. When the project first was unveiled, Barry said enthusiastically: "Any mayor would welcome this kind of Christmas present to his city."

Under Cecchi's revised plans, the Ramada Hotel would be cut from 910 rooms to 850 and the cost of the project from $240 million to $220 million. He said that most of the trimmed floor space would be pared from the top two floors of the 130-foot-high complex, which now will be staircased "like a wedding cake."

"The outside observer will not notice much difference," he said.

Cecchi said that even with his lenders' concerns about the long-term use of the complex as a high-technology trade mart, "our goal is a successful trade center." He added, "The likelihood is very remote" that it will not succeed.

High-tech trade marts have opened in Dallas and Boston with mixed success. Cecchi said that "advanced negotiations are currently under way with several major high-tech users interested in establishing substantial presence in Techworld," but he declined to name them.

While opting for the smaller complex, Cecchi took a swipe at the city's drawn-out construction approval process. He said that originally he had hoped to start construction last December and that the delay has cost his firm from$1 million to $1.5 million.