The D.C. Zoning Commission, in a decision angering preservationists and developers alike, voted yesterday to curtail high-rise commercial development on an historic three-block section of Connecticut Avenue north of Dupont Circle.

By a vote of 3 to 1, the commission decided to reduce the permitted height of buildings from the current 90 feet to 70 feet, which would allow structures up to six storeies. Most existing buildings, dating from the late 19th Century, are three to five stories high.

The new height limit could still permit significant development along both sides of Connecticut Avenue from Dupont Circle northward to Florida Avenue, Washington's historic 19th century city boundary. The limit does not apply elsewhere in the city, but could set a benchmark for other areas adjacent to downtown commercial areas where the maximum allowable height is generally 130 feet.

Spokesmen for citizen groups, who had fought to maintain what they described as the historic human-scale neighborhood, assailed the commission vote. "It's a horrible zoning. It just won't save anything," exclaimed Ann Sellin of the Dupont Circle Citizens Association, a leader in the decade-long fight to reduce the permissible height to 50 feet.

Whayne S. Quin, a zoning lawyer with clients in the Dupont Circle area, said the decision "is not in the city's best interests" in maintaining economic competition with the burgeoning suburbs. By reducing tax incentives to developers, he said the change in zoning would probably hasten the demolition of older buildings rather than help save them.

While almost certainly decisive, yesterday's vote was not final. The action is subject to review and comment by the National Capital Planning Commission, which is responsible for monitoring the federal government's interest in the capital city. That commission previously had recommended that the city zoning body adopt a 55-foot height limit north of Dupont Circle.

The ruling will take effect only after a final Zoning Commission vote, probably next month. After final adoption, it could be appealed to the courts by those objecting to its provisions.

The outcome of yesterday's vote became obvious as soon as commission members began debating the issues. George M. White, the architect of the Capitol, who by law sits on the commission, argued at first that the existing 90-foot height limit reflects proper planning and would help support the Metro subway, which served the area. But he eventually voted for the 70-foot limit.

Commissioner Ruby McZier, a lawyer, asserted that it is the job of the Joint Committee on Landmarks, not the Zoning Commission, to preserve historic structures. As a result, she said the commission had no responsibility to set the 50-foot limit the citizens wanted to save most existing buildings.

Another commissioner, Walter Lewis, a Howard University urban planning professor, agreed with McZier, declaring that "like it or not, there is another body charged with preserving the historic fabric -- the law does not give us that responsibility." He proposed the C3-B zoning that was adopted, which permits a 70-foot height.

The only vote against Lewis' motion was cast by John Parsons, associate regional director of the National Park Service, who said it would be "unconscionable" to let developers change the face of the neighborhood. He said the fate of 45 buildings is in question.

Theodore Mariani, the commission chairman and an architect, left the room during the debate and did not vote because he is a Dupont Circle property owner. He previously had favored keeping the 90-foot limit.

The reduction in allowable building heights would reduce the amount of floor space in a building that could be rented or leased. Preservationists contend that is only part of their concern, saying that they want to maintain the mansard roofs, scrolled gables and chimneys that give the area an almost European ambiance.

Dupont Circle, one of Washington's best-known public plazas, is the hub of a neighborhood of stores, galleries, theaters, offices and restaurants with a large population of professionals attracted by its diverse lifestyles.

"If historic preservation is the objective, then you should determine what buildings should be preserved," zoning lawyer Norman Glasgow asserted in arguing at earlier hearings to keep the existing height limit.

Two buildings on Connecticut Avenue already have been built to the currently allowed 90-foot height, and another high-rise development is under way on adjacent Hillyer Place. "I think Hillyer Place is a disaster to the development of that area," Parsons said.

While Dupont Circle preservationists received a setback, residents of the Fairlawn neighborhood in far Southeast Washington won a victory in a less visible, but equally controversial dispute over a proposed high-density residential development.

After six hearings conducted over a two-year period, the commission voted 4 to 1 to reject a 100-unit project on the vacant site of the former Ruppert Home for the Aged at 22nd Street and T Place SE. Only Mariani voted to approve it. A total of 52 units could be built on the site under existing zoning, but there are no plans for that size project.

"We spent a lot of time, a lot of hours [fighting the project] and we are elated," exclaimed Ron Moyer, a Fairlawn Advisory Neighborhood Commission member.