Since 1891, SHE has reigned among the graves, the most mysterious and serene of all this city's statues. Too few of us have seen her. Enthroned in her green holly grove -- in Rock Creek Cemetery's quiet -- she meditates on life, on death. Beneath her hood of bronze her shadowed face is calm. The question she poses does not have an answer. Nor does she have a name.

She is young yet old as time. The stone on which she sits seems to be the Rock of Ages. She raises her right hand perhaps to draw a veil, perhaps in benediction. Her heavy robe suggests the shroud, but she does not grieve.

Alexander Woolcott called her "the most beautiful thing ever fashioned by the hand of man on this continent." Soames forsyte, the fictional hero fo John Galsworthy's Forsyte Saga, thought her "the best thing he had come across in America." Galsworthy, who speaks through Soames, has spent hours in her presence. "Three times he had changed his position on that crescent marble seat, varying his sensations every time. From where he was now the woman had passed beyond grief. She sat in a frozen acceptance deeper than deat itself . . . A red-oak leaf fell to his lapel, another on to his knee; Soames did not brush them off. Easy to sit still in front of that thing! They ought to make America sit there once a week."

She was fashioned by a master -- the American sculptor Augustus Saint-Gaudens (1848-1907). She guards two unmarked graves.

In one lies Henry Adams -- John Quincy Adams' grandson, great-grandson of John Adams -- who died, in 1918, the most elegantly erudite of Washington's grandees. In the other lies the body of Marian Hooper Adams, his wife of 13 years, who kolled herself with poison. His autobiography, "The Education of Henry Adams," does not mention Marian.He remembered her in silence. She died in 1885. Thereafter Henry Adams never spoke her name.

Nor would he name the gravesite statue he commissioned. He insisted that no dates, no letters or inscription mar her cemetery grove. Some called her Grief, others Mourning or Despair, but Adams would have none of it. "Do not allow the world to tag my figure with a name," he wrote the sculptor's son in 1908. "Every magazine writer wants to label it . . . Your father meant it to ask a question, not to give an answer, and the man who answers it will be damned to eternity, like the man who answered the Sphinx."

The public could not bear such doubt. Adams, and Saint-Gaudens, too, and Stanford White, the architect who designed the statue's sanctuary, were begged for explanations: What does the figure mean?

"It is curious," Adams wrote in 1903, "that what would have been elementary to every other age of mankind, and which any beggar of Benares or of Tokio would read at a glance, is a sealed mystery to the American mind."

Once, seated there before her, in what he came to call "my happy home in rock Creek," the aging Henry Adams "distinctly" heard her speak. "Futile Infinite!" she seemed to say, "I'm the stronger of the two." "What puzzles me," Adams wrote Saint-Gaudens, "is whether the figure says this to me, or I say it to the figure. I never shall know . . . I have gone on studying and reading and thinking for many years without ever finding an answer to the question which is the absolute, the ultimate, the universal -- Infinity or Finity?"

Part Fate, part Pieta, Saint-Gaudens' seated figure is part Buddha in Nirvana. Her lineaments are Western but her calm is of the East. "It is difficult," the sculptor wrote the year before his death, "to say just what I intended to express. Perhaps The Peace that Passeth Understanding is as near to it as I can get in words."

The recent cast of the Saint-Gaudens statue that now sits, as if abandoned, in the courtyard of the National Museum of American Art gives no hind of her power. The figure in the grove is one of the three most compelling pieces of American art on view in this city. The Thomas Eakins portrait of "Miss Van Buren" at the Phillips collection and the Lincoln on the Mall by Daniel Chester French -- two other seated figures absorbed in contemplation -- are her only peers. The Saint-Gaudens in Rock Creek Cemetery -- which, incidentally, lies far from Rock Creek Park between North Capital Street and New Hampshire Avenue NW -- is the least familiar and the most universal. It deserves to be seen. CAPTION: Picture, Saint-Gauden's statue in Rock Creek Cemetery; photo by John McDonnell