A half century ago this month, when the world seemed in danger of destruction, diplomat Robert Woods Bliss and his wife, Mildred Barnes Bliss, tried to plant a small seed of civilization. They gave their Georgetown estate, Dumbarton Oaks, and its precious book and art collections to be kept and cultivated by Harvard University.

After Pearl Harbor half of the house was lent to the National Defense Research Committee, while the other half continued to serve art scholars. "One works for the development of the most hideous activity of war, the other for the discovery and preservation of the beauty of human expression," Bliss said later.

In August and September 1944, the wise men of the United States, the Soviet Union and China came to Dumbarton Oaks in hope of building the foundations of "a just and lasting peace," as then-Secretary of State Cordell Hull said. Out of these discussions came the United Nations.

None of this history is on the bronze plaque at 1703 32nd St. NW. Instead, it states the heart of the Blisses' reason for giving their estate and a $20 million endowment to found the Dumbarton Oaks Research Library and Collection: "that the continuity of scholarship in the Byzantine and Mediaeval Humanities may remain unbroken to clarify an ever changing present and to inform the future with wisdom."

Dumbarton Oaks celebrates its 50th anniversary this month in much the way it usually celebrates, with seminars on its subjects and with concerts. No banners will fly, no hoopla will be heard. Dumbarton Oaks is a quiet place where no one jumps, especially not to conclusions.

Angeliki Laiou, former chairwoman of the Harvard history department, now presides over this legendary fiefdom and its annual budget of $6 million.

A window behind her desk overlooks the most formal of Georgetown gardens. Two pots of orchids from its greenhouse sit on her desk. The marble mantel is carved with an allegorical scene and a Georges Rouault clown hangs above it. Oriental rugs warm the floor.

In an adjoining oval chamber, trompe l'oeil in the classical style decorates the walls, and bookshelves are filled with real and faux tomes, some covered in illuminated leather. Lunch is set on hand-painted china.

The most beautiful room of the house, the Garden Library, not open to the public, is a sunlit bower of bow windows hung with paintings by Jean Edouard Vuillard, among others. The staircase to the offices on the second floor is festooned with iron birds, squirrels and a garden of flowers.

"I regret," said Laiou, "I don't serve tea every afternoon, as Mrs. Bliss did." Still, the staff of about 60 and the 20 or so scholars and favored guests every day at lunch are encouraged by chef Wendy Marcus to take up matters of taste in more than one sense.

Laiou came to Dumbarton Oaks a year or so ago for a five-year term. She, her economist husband, Stavros B. Thomadakis, and their 16-year-old son live in a grace-and-favor house on the property.

"Dumbarton Oaks is a very complex place," she said, because the Blisses "thought that humanist endeavors engage more than the intellect." They believed, she added, that "quiet study and contemplation would be aided by the serenity of open spaces and ancient trees."

The 16 acres, 10 of formal gardens with distinguished garden architecture, bloom with magnolias, cherries, spring bulbs and autumn chrysanthemums to serve Dumbarton Oaks's most public role, as a garden oasis, slaking the thirst for beauty and quiet in a 20th-century city.

Its Byzantine collection includes 1,492 artworks and 107,623 books; its pre-Columbian holdings, 685 objects and 17,832 volumes; the Garden Library, 13,000 garden books.

Yesterday, some 250 Byzantine scholars from all over the world came at the invitation of Laiou and Harvard President Derek Bok for a seminar on Byzantine civilization.

A seminar last month took up Bliss's importance in recognizing that works of this period were "objects of fine art," said Elizabeth Boone, the pre-Columbian collection's director..

On Jan. 13 and 14, the Twentieth Century Consort will perform Stravinsky's "Dumbarton Oaks" Concerto in the great music room with its 16th-century stone chimney piece, 18th-century parquet floor and elaborately painted ceiling in the 16th-century French mode.

In 1894, when Robert Bliss was 18 and Mildred Barnes 14, his father married her mother. The younger Blisses married in 1908 and began 54 years of collecting art and books from all over the world. Bliss served 33 years in the Foreign Service, finally as ambassador to Argentina. Mildred Bliss, heiress to the Fletcher's Castoria fortune, was one of the "3-B's." She, Marie (Mrs. Truxton) Beale and Virginia (Mrs. Robert Low) Bacon presided over Washington society from their historic houses.

Their interest in Byzantine art -- A.D. 326 to the fall of the empire in 1453 -- began in the 1930s at an exposition in Paris. They collected icons; notable 6th-century ecclesiastical silver vessels; a 6th-century gold and blue enamel cross, to mark their 50th wedding anniversary; mosaics, some set in the floors, and even a mosaic pool. Their collection of Byzantine coins is one of the largest in the world.

When Bliss resigned from the Foreign Service in 1933, they came back to Washington to live in their country house in the city. They named their estate for its oaks and its history.

The land on which Dumbarton Oaks was built, in what eventually was called Georgetown Heights, was owned by Col. Ninian Beall of Maryland in 1703. He called his plantation the Rock of Dunbarton, a misspelling of the Rock of Dumbarton near Glasgow. William Hammond Dorsey bought a parcel of it on what is now R Street and built a brick house in the Federal style about 1801. Secretary of War John C. Calhoun later owned the house and in 1824 was host there to the Marquis de Lafayette.

The Blisses had bought the house in 1920 and hired Frederick H. Brooke to strip off the Victorian fripperies it had acquired and add the music room, and Beatrix Cadwallader Jones Farrand to design the garden. Mildred Bliss is credited with a heavy hand in both undertakings. Philip Johnson designed the charming domed circles of the pre-Columbian gallery to her taste. Recently, Hartman and Cox closed in an atrium and built underground book storage.

Robert and Mildred Bliss lived in the house for only seven years, moving to a smaller house on 28th Street after they gave Dumbarton to Harvard. But in 1958, they celebrated their 50th wedding anniversary in the garden, and the guests lined up clear to Wisconsin Avenue.

The galleries at Dumbarton Oaks are open from 2 to 5 p.m. daily except Mondays, and the gardens are open daily November through March from 2 to 5 p.m. and April through October from 2 to 6 p.m. Concerts are by subscription.