The Girl Scouts of America have agreed to sell Rockwood, their wooded, 92-acre scouting center near Great Falls, Md., to a developer who plans to build houses on the land.

A spokesman at Girl Scout headquarters in New York said the organization's board of directors voted to sell the land, left to the scouts in 1936 in the will of a wealthy Washington socialite, because costs of equipping, staffing and operating the center have become excessive.

The facility, at 11001 Mac-Arthur Blvd., is called the Rockwod Girl Scout National Center and is used by Girl Scouts from across the country for seminars, training sessions and athletic programs. An estimated 20,000 girls pass through the center each year, a Girl Scout spokesman said. In future years, girls who would have gone to the Rockwood center will go to a similar facility in Westchester County. N.Y.

The tract is one of the few remaining large parcels of wooded land in the Potomac area. It is near the C & O Canal and the Old Angler's Inn, a local landmark.

Neither Girl Scout headquarters nor the developer, Berger-Berman Builders Inc., would disclose the sale price. Observers estimated that the property is worth at least $20,000 an acre, which could bring the price to over $1.8 million. Some property in the Potomax area sells for as much as $60,000 an acre.

Peter Berman, president of the development firm, said he plans to build homes worth more than $100,000 apiece on the site. He said he will attempt to preserve as much of the woods as possible.

Current zoning would permit construction of homes on half-acre lots, permitting the company to build up to 180 homes.

One possible obstacle to development is the need to obtain from Montgomery Country Permission to apply immediately for sewer service. Under its current status, the tract is not scheduled to receive sewer service for several years.

A spokesman for County Executive James P. Gleason said Gleason is opposed to any change in the sewer service category of the land at this time.

Berman said he may be forced to install septic systems instead of public sewer service, out that this would cause him to "denude" a larger portion of the property of its trees.

The land was willed to the Girl Scouts in 1936 by Carolyn G. Caughey, a Washington socialite and real estate woman who specified that if the scouts should ever "abandon" the property or cease to use it for a "character building" purpose, it must be turned over to the Esther Chapter of the Eastern Star, a Masonic group.

Harold Grier, a lawyer who represents the Esther Chapter, said the Girl Scouts asked the organization last Friday to waive its rights to the property.

Grier would not say specifically why Eastern Star agreed to waive its rights, but he said one "could assume that the Girl Scouts would not relinquish their interest in the property unless we relinquished our rights to it."

He added, "the chapter has full confidence in the Girl Scouts . . . I'm sure (the money from the sale) will be used for a good purpose."

A spokesman for the Rockwood Center said the facility will close Sept. 30.