Tregaron, the last large undeveloped tract in Northwest Washington finally was sold yesterday, but not before a last-minute squabble in which heirs to the property opposed to the sale accused those favoring it of secretly arranging the final settlement of the $4.6 million transaction.

Under terms of the sale, achieved after years of bitter sparring among the owners, the Washington International School will continue to use the elegant Georgian mansion at Tregaron and the surrounding grounds as its headquarters. gMeanwhile, a development firm says it plans to build about 200 luxury town houses worth more than $200,000 each on none of the 20 heavily wooded acres, while six acres will remain undeveloped.

But some wealthy Cleveland Park residents, who live near the Tregaron site at 3100 Macomb St. NW and use the estate's rough terrain as their own private park, immediately said they would try to block Tregaron Development Corp.'s plan to build clustered town houses on the property.

Lawyers met yesterday afternoon at a downtown realty company to work out final details of the Tregaron sale, ordered last June by D.C. Superior Court Judge Milton D. Korman over the vociferous objections of a lawyer for three of the six heirs to the property.

Korman's order seemingly ended a decade-long, highly publicized family feud among the descendants of Washington lawyer Joseph E. Davies, the controversial ambassador to Moscow before World War II, a self-made millionaire husband of cereal heiress Marjorie Merriwether Post and the grandfather of former Maryland senator Joseph D. Tydings, one of the heirs who supported the Tregaron sale. Two other heirs sided with Tydings in favoring the sale, while three other Davies descendants strenuously opposed the sale because they believed the property was worth substantially more than the $4.6 million selling price.

After Korman's order, and a later D.C. Court of Appeals order that ended a last-ditch attempt to block the sale, the Tydings heirs, the school and the development firm moved toward a final settlement of the sale. However, the three dissenting heirs did not learn about yesterday's property settlement until they were questioned late yesterday by a reporter.

"We've been sinned against," fumed Suzanne Walker Wright, one of Davies' grandaughters and an opponent of the sale. "It is a travesty of justice, a miscarriage of justice. I'm not a little angry, I'm very angry."

Nicholas A. Addams, an attorney representing Wright and two other heirs who objected to the sale -- Emlen Davis Evers of Cleveland, one of the two Davies daughters still living, and Wright's sister, Jennifer Fitch Moleon -- said he recently had requested that the D.C. Court of Appeals reconsider its order two weeks ago lifting its ban on the sale.

Tydings, his mother, Eleanor Davies Ditzen, and his sister, Eleanor Tydings Schapiro, supported the sale. "I think that my grandfather would have been pleased that the big house will be used for a very worthwhile purpose by a fine institution, the Washington International School, and that the integrity and beauty of the property will be preserved," Tydings said.

Schapiro said Tregaron "has caused a terrible [financial] drain on the family throughout the years, so we hope to get something out of it. Maybe the family will settle down and be friends again."

E. David Harrison, Tregaron Development's attorney, said the proposed construction might begin within 18 months and plans call for dense clusters of town houses around courtyards surrounded by the estate's remaining trees. "Every unit will have a view of the trees," he said.

A feisty group of Cleveland Park residents, who live in $200,000 turn-of-the-century homes and highly value the Tregaron greenery, said they would continue their opposition to development of the estate, located just west of Connecticut Avenue NW.

"It's not the end of the fight," said Sheldon Holen, chairman of a 20-member neighborhood organizing committee. He said the group would try to block the developer from obtaining the necessary rezoning from the city government or changing the tract's historic landmark status.

If that fails, Holen said, "We'll have the kids lie down in front of the bulldozers."

One winner in the long Tregaron battle is the Washington International School, which has occupied the stone-columned mansion on the estate since 1972. The school has more than 300 pupils in grades four to 12 at Tregaron, of which about half are foreign nationals and 16 percent inner-city youths on full scholarships. Washington International requires its students to become proficient in either French or Spanish and its classes are taught in those languages one day and English the next.

School director Dorothy Goodman declined to disclose what portion of the purchase price the school paid, but said financial assistance was provided it by the Ford Foundation.