Two federal planning agencies are strongly opposing proposed zoning changes to permit construction of 120 town houses on the historic Tregaron estate, the largest remaining undeveloped tract in Northwest Washington.

The National Capital Planning Commission, at a meeting last week, joined an earlier decision by the Joint Committee on Landmarks in opposing the development because of fears that the large number of houses would mar scenic and historic values of the 70-year-old mansion, the adjacent Klingle Valley Parkway and the Cleveland Park neighborhood.

The action by the planning commission, the federal planning agency for the District, was supported by numerous community groups but dismissed by E. David Harrison, attorney for the developers, as the quirky, "novel" opinions of "two quasi-federal agencies whose opinions are only advisory."

The real battle over the future of the hilly, heavily wooded estate near Connecticut Avenue and Macomb Street NW begins Oct. 4 before the D.C. Zoning Commission in what is expected to be three or more hearings.

The Tregaron Development Corp. is asking for rezoning and planned unit development, or PUD, status of its 14.6-acre site to allow more houses than present zoning permits on hillsides below the Tregaron mansion.

Under a 1980 court settlement, the house and 4.6 acres of the original 21-acre Tregaron estate of Joseph E. Davies, a former ambassador to Russia, were sold to the Washington International School.

The developers last year proposed a 180 town-house development on its site but dropped that to 135 and then 120 houses after criticism from the Joint Committee on Landmarks, the federal-city agency that oversees historic landmarks in the District.

Both Tregaron and Cleveland Park are designated as national historic "Category III" landmarks, worthy of protection if possible. (Rock Creek Park and Klingle Valley are landmarks of a higher category.)

Harrison insisted the present town-house development plan is relatively modest "since we're planning to use less than 13 percent of the site." He predicted, "I think we will be granted almost exactly the PUD we've requested" from the Zoning Commission.

After Harrison appeared before the planning commission in April, the developer, responding to criticism, modified plans to add a retaining pond to catch rainwater and keep construction runoff from entering Rock Creek, reduced the number of parking spaces and paved area and moved some proposed houses from the steepest slopes.

Harrison argued at last week's planning commission meeting that an old bridge, roads, old stone walls and 92 percent of the estate's trees, which officials had expressed concern about, are being preserved. He contested the commission's right as an agency to protect "scenic values."

Planning commission executive director Reginald Griffith noted the commission had expressed similar concern over the dense cluster-home development of Hillandale beside Rock Creek Park, another of the city's old estates recently sold for housing developments.

Opponents of Harrison's development cited it and Hillandale as examples of overdevelopment next to parks.

Peggy Robbins of Advisory Neighborhood Commission 3C said the ANC and most civic groups do not oppose town-house development of Tregaron, but they want fewer houses -- 68 was mentioned frequently -- and a larger buffer of woods between the houses and Klingle Valley Parkway.

Richard Ridley, architectural consultant to the Friends of Tregaraon, a group of 200 area residents formed to fight for less intense development of the estate, told the planning commission that 60 to 70 houses could be built without a significant impact, but that 120 houses was double the density of surrounding Cleveland Park and would overwhelm the hilly site and nearby parkland.

Elizabeth Rowe, a former planning commission member, spoke for the Committee of 100 on the Federal City, Washington's oldest planning group. "We feel very strongly this is an overdevelopment," she said.

Philip Padgett of the Woodley Park Towers Condominium Association said its 232 members were not opposed to development of Tregaron, but "this egregious intrusion" of 120 houses would be prominently visible from Klingle Parkway and would detract from the park. The condominum is opposite the estate on Kingle Valley Parkway.

Two planning commission members, Bruce Kirschenbaum and Marian Morris, voted not to oppose the development.

James Gibson, the mayor's representative on the planning commission, left during the debate and did not vote. His Office of Planning and Development will make its own recommendation on Tregaron to the D.C. Zoning Commission.