IN ITS WAY, the "Roundel of the Seasons" may turn out to be the same kind of breakthrough as Manet's "Luncheon on the Grass" or Louis Sullivan's Wainwright building.

Is calligraphy an art? In the Orient it has been accepted as high art for centuries. But in the West -- until just a few years ago -- it was basically a social grace, an elegant accomplishment for gentlewomen. To this day, the handwritten invitation has a certain cachet in Washington, and guest lists for state occasions are farmed out to calligraphers all over town.

But an art?

Sheila Waters is marketing her roundel as a Cibachrome print, in editions of 500 and 750, depending on size, at $75 and $45. Her husband Peter did the terribly exacting photographic work in his home darkroom.

The point is, this elaborately illuminated piece of work, about a foot square and representing 1,000 hours of meticulous labor, is assumed to be art, as much as any 17th-century Chinese poetry scroll.

And what makes it different from any other fancy script turned out in a Smithsonian calligraphy course?

You have to study it with a magnifying glass to believe it. The roundel has 12 medallions showing the Zodiac signs. The colors change smoothly from blue for winter through the scale to yellow for summer. Seasonal flowers grace the empty spaces, and on the inner ring, among the names of the seasons, are tiny seasonal features: squirrels and acorns, a snowman and Christmas tree, a girl in a bathing suit ("our bit of erotica," mutters the artist), all in colors so carefully controlled that when you look across the circle you find the complementary color.

The lettering around the core, "And God said, Let there be light, and there was light," changes color too. "I wanted the letters to dance, like flames," says Waters. And they do. Outside it is the ancient Egyptian Hymn to the Sun: "Shining in the sky, a being as the sun, he makes the seasons by the months: heat when he desires, cold when he desires; every land is in rejoicing at his rising every day." And, delicately ringing the whole structure, a miracle of precise fitting that shows no sign of crowding, is the famous passage from Ecclesiastes: "To every thing there is a season . . . "

In the four corners are quotes about the seasons from the Song of Solomon, Donne, Camus and, of course, "Sumer is icumen in."

"It represents about 4 1/2 months of solid work. I used up six fine watercolor brushes and got a backache. I started in January, and by August I had to get new glasses with a nine-inch focus. Normally I don't wear them -- my eyes are just fine. The ophthalmologist bought one of the roundels."

Sheila Waters wants to make it perfectly clear that she is not your garden variety calligrapher. She had six years of art school training in England, culminating with the equivalent of a master's degree from the Royal College of Art. She has logged many hours with the Book of Kells, a major influence on her work (which in fact does resemble medieval illumination in its intricate pointillism) and the Lindisfarne manuscript. A 20-year veteran of the Penguin Books map department, she was one of the handful of top British calligraphers called upon to inscribe the names in the RAF roll of honor at St. Clement Dane Church in London.

"I wrote more names than anybody," she says, "60 names to a page, 300 pages to a volume, 35,000 names. I worked on it six years at home; the children were little then, and it was an ideal job."

There are three children, grown now, and Sheila and Peter Waters live on a three-acre tract near Gaithersburg where every summer people come from all over the country -- "San Diego, Vancouver, Miami, Houston, New York" -- to camp on the lawn and take her two-week course in calligraphy. By the way, she founded the Smithsonian's calligraphy program. Her husband, conservation officer at the Library of Congress, was brought to this country by the library after doing pioneer work in restoring five centuries worth of books damaged in the 1966 Florence flood.

The roundel is on exhibit at the Quill and Brush Gallery in Bethesda. The artist, still busy with production, hasn't yet thought of a new project.

"When I finished with this, all I wanted to do was get a great huge brush and paint a mural or something," she sighed.