The Joint Committee on Landmarks has unanimously opposed the proposed rezoning of a historic three-block section of Connecticut Avenue north of Dupont Circle, saying it would encourage demolition of the turn-of-the-century buildings that line the avenue there.

The new zoning -- given preliminary approval by the D.C. Zoning Commission two weeks ago -- would act as an "incentive for razing the existing structures . . . and replacing them by taller and greater density buildings," the joing committee said. The agency is the official review board for actions affecting Washington's historic landmarks and the city's 14 historic districts.

A divided zoning commission, which will take its final vote on the issue in April, is considering the new zoning for the section of Connecticut Avenue between Dupont Circle and Florida Avenue in response to the citizens' petition for new zoning regulations. The zoning would lower the height of buildings from the currently allowed 90 feet to 70 feet. It also would slightly reduce the maximum square footage of future buildings.

But the joint commission, the National Capital Planning Commission and civic groups oppose the zoning change becuase they fell it doesn't go far enough in protecting historic structures in the area, most of which are 40 to 50 feet high.

The joint committee and the planning commission -- federal agencies that have only an advisory role in zoning mateters -- have recommended that a special zone be created to protect this and other historic districts in the city. In the meantime, they recommend that the commission pass a C-2-A zone with a 50-foot height limit to protect the Connecticut Avenue neighborhood. This type of zone also would permit office buildings of only about half the size of square footage of those permitted under the C-3-B zone tentatively approved by the zoning commission.

If a 50-foot height limit were imposed, there would be less incentive for owners to demolish the old buildings and more incentive to restore them, say civic groups and the Neighborhood Advisory Commission, which represents many of the 18,000 residents living in and around the Dupont Circle Historic District.

The Dupont Coalition of seven neighborhood civic groups "has been attempting for eight years to get the area rezoned," coalition spokeswoman Anne Sellin told the joint committee last week. She urged the committee to oppose a 70-foot height limit, saying it would create "a great incentive to demolish" the more than 50 late 19- and early 20th-century buildings along the avenue.

Under the present C-3-C zone, four large office buildings have been built within the historic district and two more -- 74 and 88 feet high -- recently were approved. Several historic buildings were demolished to make way for them.

Only one of the five members of the Zoning Commission, National Park Service representative John Parsons, opposed the 70-foot height limit. In the 3-1 vote, outgoing commission member Theodore Mariani, an architect and Dupont Circle property owner, excused himself. The commission may have a new member by its April meeting, Woodley Park citizen activist Lindsley Williams, who was nominated recently by Mayor Marion Barry. The City Council has scheduled a confirmation hearing on the appointment for March 19.