The forester has measured and counted the trees, the traffic consultant has clocked the cars, the economist has turned in the market study, the site planner has prepared the drawings, the sociologist has started studying the neighborhood. Now the lawyers have been hired to begin turning Hillandale, the 42-acre John Archbold estate on Reservoir Road NW, into one of Washington's most exclusive housing developments.

Forty-five detached homes and 230-three- and four-story town houses -- with elevators to ease the climb from the underground parking garage to the rooftop deck -- are proposed for the planned unit development (PUD) scheme that will be submitted to District planning agencies later this month.

With prices starting at $225,000 for the smaller town houses and ranging up past $350,000 for the single-family homes, Hillandale is expected to be a $70 million development.

It is being planned by Hillandale Development Corp., a subsidiary of Tecon Realty Corp., a California company that in turn is a subsidiary of Tecon Corp. of Dallas. The whole family of firms is owned by Clint Murchison Jr., the Texan who owns, among other things, the Dallas Cowboys and Centex, a major home builder in the Washington suburbs.

The vice president of Hillandale Development and the man in charge of the project is Michael L. Gulino, who recently set up shop at 1101 Connecticut Ave. NW.

Hillandale Development last summer signed a 99-year lease on the Archbold estate, which is the largest tract of privately-owned undeveloped land in the District of Columbia.

The estate is north of Reservoir Road opposite Georgetown University Hospital; its eastern boundry is 39th Street NW; the west side borders on Glover-Archbold Park, which was part of the Archbold property until it was given to the National Park Service.

The plans call for keeping the Archbold home -- a modern replica of an Italian villa -- either as a community center or a private residence and also keeping the similiarly-styled gatehouse at the Reservoir Road entrance.

That entry is to be closed and replaced by a single drive off 39th Street just south of S Street, where a new gatehouse will control access to the development.

Clusters of town houses are proposed for the south and east sides of the property and west of the main house. Along the rear of the tract, abuting Whitehaven Park, are lots for 45 detached houses; Hillandale officials say those sites may be offered for custom houses.

The town houses, Gulino said, will range from 2,500 to 4,000 square feet and will be grouped around court-yards; beneath the courtyards underground garages are planned.

The plans also call for swimming pools and tennis courts, plus three ponds that would do double duty as scenic amenities and drainage control basins. All these facilities would be owned by a homeowners' association.

Architects for the project will be hired in the next few weeks, Gulino said. Construction is expected to start in 1980, with the town houses to be built in three phases over three years.

Unless the Archbold family exercises its option to sell the property to the Murchison interests, the development will be the first major housing project in Washington to be built on leased land. Setting the legal foundations for building on leased ground was the first problem for the developers' law firm, Linowes & Blocher.

The job of getting the project through the District's complex PUD approval process will be handled by a new member of the Linowes firm, former city planning director J. Kirkwood White. The PUD application will be submitted as soon as the City Council completes action on a new PUD law that was drafted before White left.

The Archbold property is zoned for the same kind of single-family row houses that line the streets of neighboring Burleith. The zoning would permit 296 houses to be built on the estate, but filling Hillandale with rowhouses on 20- by 100-foot lots would require cutting most of the trees and leveling the rolling hills and meadows that gave the estate its name.

Instead the developers are proposing to build about 20 houses less than the maximum, cluster them, and preserve as many trees as possible, leaving untouched the steep slopes that have made the estate a favorite play area for children brave enough to climb its fences.

That doesn't require a zoning change, but it does require municipal approval of the PUD plan and two public hearings.