EVERY DAY, for an hour at least - it once was longer but her legs are not what they were - Marjorie Phillips paints at the great easel in her studio. Today the painting is a self-portrait, "Finished, but does it need just one more brush stroke? And tell me, do you think it looks too young?" No, rested perhaps, but not too young.

Light streams into the northwest octagonal-shaped wing of her Foxhall Road mansion - every artist knows about the "good north light," steady on, morning to night, winter to summer.

This is Phillips' 81st year, and the first one-person show of her painting ever held in a Washington commercial gallery opened this week at the Franz Bader Gallery, 2124 Pennsylvania Ave. NW.

Phillips is one of those artists who make you believe the legend that artists live long lives to work best in their later years, unlike writers and composers who tend to bloom and wither early. She hasn't counted how many pictures she has painted, since she started to paint as a young girl. But in her Bader show are 20 paintings, most of them from the last decade.

These gentle pictures of flowers admired and landscapes remembered are all primarily studies of colors. Her paintings have a restrained cheerfulness, as though one must keep one's spirits up by contemplating beauty, while remembering that life is not always a pot of tulips. Neither Phillips nor her paintings are assertive; they are quite restrained, a bit shy, but with a certain strength from being loved and taken seriously.

Her paintings, until the Bader show, hung in her 18-acre mansion, the eighth most-expensive estate in the District of Columbia, assessed at well over $1 million. Her paintings hang in her house along with those of Pierre Bonnard over the drawing room fireplace and sofa and Pablo Picasso in the dining room. The curving drive leading to the house passes through a fence with its warning signs about protective devices.

"I had to hang mine after it was no longer possible for legal reasons to borrow paintings from the Collection, as we used to. For years, of course, when anyone was coming to lunch, we'd borrow a picture from the gallery that we thought they'd particularly like. The Bonnards and the Picasso will some day go to the Collection."

The Phillips Collection, originally a memorial to her late husband Duncan's father and brother, was the first museum of modern art in the United States. It opened in the fall of 1921, shortly after she and Duncan came back to Washington from their honeymoon. Marjorie Phillips' paintings also hang in the Phillips Collection, along with Renoir's "The Boating Party," and all the other masterpieces she and her husband collected in more than a half-century.

It seems strange now, speaking to this gracious lady, her hair salted with gray, that once she and her husband were adventurers in art, introducing strange and frightening cultural concepts to the United States. In the beginning were the Phillipses, before the National Gallery of Art (of which he was a founding trustee), before the Hirshhorn, before the National Collection of Art. Only the Corcoran Gallery came earlier. The Phillips family fortune is old money, originally from steel mills.

They lived "above the store" on the third floor of the family home and art gallery on 21st Street until 1929, when they built their fine home on Foxhall Road, then Washington's country place.

"I had a studio even in the old house," she said. "My husband liked for me to paint, and always encouraged me. I painted on our honeymoon, while he thought about opening the gallery. When Nathan Wyeth, (an old-time Washington architect) designed this house, my husband told him, it must have a studio for me."

The closeness of Marjorie and Duncan Phillips, an old love story, can be plainly seen still in that northwest wing where they had their ateliers, near enough to be cozy, separate enough for serious work. You can look at the juxtaposition of the rooms and imagine him coming to the door, while she was painting, and reading her a paragraph he'd just written, and then taking a look to see how her picture was coming along.

The octagonal wing is divided into two parts. His study where he wrote his books of criticism has a tile-surrounded fireplace, a landscape by his wife above it, an Eero Saarinen womb chair and a Mies van der Rohe/Lilly Reich Barcelona chair at either side. The study also has two fine art moderne pieces, a desk and a side table. The room could stand as a late '40s period piece. Marjorie Phillips used this room herself, after he died, to write the loving book, "Duncan Phillips and his Collection."

The other room has chairs and a fireplace too, with a splendid portrait of Duncan Phillips, painted by his wife. Any painter would envy the easel, much taller than Phillips, who herself is not a short woman. The palette, not cleaned off, still has squeezes of colors from the morning's work. Against the wall are the cheerful flower pictures, ready to go to the Bader gallery. There's nothing fancy about the room. It is a serious workroom.

"I didn't paint for a while, after Duncan died," she said later in the drawing room, over tea, coffee cake and elegant egg sandwiches. "First I had to write the book (published in 1971). And then, you know, I succeeded him as director of the Collection, from 1966 to 1972. When my son Laughlin succeeded me as director, even though he divided his time with the Washingtonian, his magazine. I thought it was time to get back to my own work. But I can't stand to paint now as long as I once could. I don't paint very fast. My husband always had the idea I could paint as fast as you could take a snapshot. When he painted it was like that, quick few strokes. And Laughlin, too.

"Laughlin doesn't like this self-portrait of me. You know, the family never likes portraits of its members. 'The nose?' 'The eyes?' 'There is something a little wrong about the mouth,' they say. But I've worked on it some since he saw it." She speaks so quietly and slowly and tells her little jokes with such a straight face, that you must listen closely, and not talk too much yourself to be sure you don't miss anything.

Painting has always been Phillips's profession. When she was a little girl, one of six children, she and the others painted and drew a magazine, with a circulation of one. She painted in watercolors at first - "harder than oils, I think, because you can't paint over them. Even when I went to oils, I would wash off my mistakes in turpentine, it took me years to learn to like the effect of underpainting."

She grew up in Ossining on the Hudson. Despite the opposition of her father, who thought artists were too Bohemian, she and her sister studied at the Art Students League in New York City. Phillips, if you stop and think of the 1920s when she was a young woman who called herself an artist, had to have a considerable strength of mind to take herself and her work seriously. But, as she herself admits, she was fortunate in having a husband who also considered her art as serious. She has shown her work in San Francisco and London, and she was honored for her art in 1973 by Smith College.

On one of her New York days, in January 1921 as she relates in her book, her uncle, artist Gifford Beal, gave her a card to a Century Club exhibition of the collection of Duncan Phillips. After all those years, she still remembers Phillips saying of an Arthur Davies painting "beauty touched with strangeness." Later, at her uncle's studio he saw one of her landscapes and bought it. She has remembered her entire life the excitement of having the eminent art collector buy her picture, experiencing it again, vicariously, when they bought other young artists' work, as they did again and again.

Marjorie and Duncan Phillips went on her first trip to Europe in 1923, and she remembers it as the happiest and the saddest of times.

Happy, because they went to lunch at the home of Paul Durand-Ruel, a great connoisseur and dealer. They were seated directly across from Pierre Auguste Renoir's "Luncheon of the Boating Party," for a good reason, they suspected. And indeed they bought the painting - for $125,000, a great prize - and it became the cornerstone of their collection.

Durand-Ruel's daughter wanted to buy a small landscape by Marjorie Phillips, but her husband wouldn't sell it.

Phillips remembers her husband taking her to Parisian restaurants - where he ordered poached eggs and bread pudding. It was one of his jokes that he had ruined his digestion at college by frequenting hot dog stands.

They were staying at that time in the Trianon Palace Hotel at Versailles so their II-month-old baby girl, Mary Marjorie, could be outdoors more. Sadly, the child was stricken with encephalitis, an illness whose effects have lasted all her life.

Many luncheons with famous artists and collectors have taken place in the house on Foxhall Road. In her book, Phillips tells about Gertrude Stein coming to dinner, and how much her husband disliked Stein's "hostility," though Phillips herself thought Alice B. Tokas was kind, and put-upon. Phillips also suggests that it was really Leo Stein, Gertrude's brother, who was the connoisseur of painting. And she remembers that Gertrude Stein, in a lecture at the gallery, said, "When in a picture gallery what I look for is a bench, is a bench, is a bench."

When Henri Matisse came to visit, a large tree was installed along the drive during lunch. He was very surprised, he said, that a tree could grow that tall during those two hours.

The dinning room of the Phillips house is in the octagonal wing on the east side of the house, matching the study/studio octagonal on the west.In a position of honor is a Picasso, an early one, a still-life, quite mild and polite, a bit wispy, as though dimly seen. She recalls they paid $40,000, a pittance compared to its worth today. On another wall is still one more Bonnard.But over the fireplace is a fine Phillips landscape, painted in Pennsylvania while they still owned a farm there.

The drawing room, and the cross hall, is in the middle of the house, linked to the matching octagons by hyphens which serve as library space. The drawing room is a grand room, of a size few people have any more. There is a Bonnard over the fireplace, of Rome, painted on the artist's only trip to Italy. By a door is a colorful carved and painted screen, by Charles Pendergast. There is a painting by a longtime member of the gallery staff, James McLaughlin, and still another Bonnard. At the other end of the room, over the Steinway grand piano, is a Phillips landscape. On a table is one of Betty Parsons' small polychromes.

As in other homes where paintings are the principal interest, the walls are only lightly colored, the furniture is simple and unobtrusive. The trim, save for repeating pilasters, is not elaborate. "We told Nathan Wyeth that we wanted a simple house," Phillips said.

The drawing room, though a large space, has a rather homey quality. The chairs are obviously arranged for conversation, and there's a table handy everywhere for your tea cup. The grandchildren, Laughlin Phillips's children - Duncan, 17, now away at school in New England, and Liza, 16, at Maderia - come to tea on Sunday afternoons here, poured from the heavy silver teapot and weakened with water from the silver kettle. Liza's own paintings are on the piano. Her grandmother thinks she paints well and truly cares about art. Perhaps, she says, she will grow up to be the Phillips director of the future.

Like all great Southern houses of a certain age, there are double doors in the drawing room, on an axis with the front doors, for the sought-after cross ventilation. The doors in the drawing room lead to a south colonnaded portico and the tulip beds, though in the corner, Phillips is experimenting with roses. It is said that in the winter you can see through to the Potomac River, though now there are too many leaves on the trees.

To one side of the 18 acres, his mother says, Laughlin Phillips has always wanted to build a house, in the grove. "The architect wanted us to build there," she remembers, "but we liked this spot better." And you can see why, because all the world seems to drop in terraces down from this spot.

From below the terrace is a good place to admire the bricks, especially handmade in Virginia for the house, the shades of red, from shrimp to a darker hue, especially chosen by Duncan and Marjorie Phillips, who always cared most about color.

Houses like this one, estates like this (Dun-Mar-Lin, for Duncan, Marjorie and Laughlin) belong to a world where Picassos cost $40,000 and Renoirs $125,000, where grandmothers give children Sunday tea, and artists at 81 work every day and have solo shows. CAPTION: Picture 1, Built in 1929 of handmade brick by the late collector and critic Duncan Phillips and his artist wife, Marjorie, above,; Picture 2, this mansion, now assessed at more than $1 million, was among the first of the great Foxhall Road estates. The paintings of Marjorie Phillips are on view at Franz Bader Gallery through May 7.; Picture 3, At tea time: The Phillips mansion drawing room hung with Marjorie Phillips' oil paintings. Photos by Charles Del Vecchio - The Washington Post