About 140 Cleveland Park residents attended a hearing before the D.C. Zoning Commission last night to voice opposition to a plan to build 120 luxury town houses on the old Tregaron estate in Northwest Washington.

A group called Friends of Tregaron, an organization of residents who oppose the development, contend that the project should be reduced by half to prevent traffic congestion in the area and preserve the historic significance of the site.

"The fundamental issue is a question of density," said Joseph T. Howell, of 2923 Macomb St. NW.

Kathleen Wood, of 2938 Macomb St., an architectural historian, called the proposal "inadequate and insensitive" to meet preservation concerns.

The Tregaron Limited Partnership is seeking a zoning change that would permit construction of more housing than is now permitted, but clustered in such a manner that it would preserve most of the trees on the sloping 14.6-acre site.

Frank Southard, chairman of the board of the adjacent Washington International School, was the only person to testify in support of the proposal at the hearing, held at the Capital Memorial Seventh Day Adventist Church, 3150 Chesapeake St. NW.

The school and the developer jointly purchased the entire 20-acre Tregaron estate in late 1980.