She had never even dreamed of being a photographer. When she was 4 1/2, she awoke from slumber and saw a tree in her room.

"How can a tree be in my room?" she asked her father.

"It's a painting of a tree," her father told her. "Your Uncle Benjamin is an artist and he can make a tree."

"From that day forth, I knew that I had to be an artist," Barbara Morgan says. She is wearing a hand-embroidered smock, a turtleneck and black pants. Her hair is silvered, her face warm. She hardly seems 81, jumping up first to mimic a bird and later to slap her bottom as an indication that she could lose a few pounds.

She rules easily in the home she and her late husband, Willard, built 40 years ago outside Scarsdale, N.Y. All the cabbies at the train station know the place as Morgan House, and some warn visitors: "Don't let her drive you around in the Volkswagen."

What they mean by this is not that Barbara Morgan is a doddering old lady who shouldn't be venturing out on the road; rather, that she is a presence to be reckoned with. Which is to say that she drives like . . . well, a cabbie.

Aside from her home-town notoriety as the blue-caped lady in the orange VW bug called Petunia, Barbara Morgan is inevitably linked, in the realm of photography, to dancer Martha Graham. They met in 1935 at a dinner party and spent the next six years together. Morgan created 128 portraits of the artist that were published in 1941 as the book "Martha Graham: Sixteen Dances in Photographs." The New York Times likened the project to "achieving the impossible." The Herald Tribune called it "stunning" and "uncanny." And photographic historian Peter Bunnell has written of Barbara Morgan's photography in general:

Her work in dance and photomontage is perhaps the most important . . . because it marks a change in the fabric of American photography. It bridges the abstract and synthetic work developed in Germany and elsewhere in the Twenties and the rigorous straightfoward disciplines generally admired in this country and practiced by two of her close friends, Edward Weston and Charles Sheeler. It is also a connective between the natural environment, which for her colleagues and predecessors was the landscape, and the interest in the human world and the urban architectonic.

Her work is currently part of the 10-woman photography retrospective at the Corcoran. And today she will be the guest of honor at a public reception from noon to 2 p.m. at the Kathleen Ewing Gallery, 3243 P St. NW, where a show of her work opens for five weeks.

Morgan grew up in southern California, an 11th-generation American whose ancestors arrived in Massachusetts just after the Mayflower landed. Her mother was a schoolteacher; her father, a peach farmer who raised his crops organically. They read poetry and Darwin to each other, and young Barbara learned more from keeping her bedroom door open a crack than she did later at UCLA studying art history and painting.

Her father subscribed to National Geographic and Scientific American. She recalls that when she was 5, he picked up a pebble and asked:

"Do you think this is moving?"

"No."

"Guess what's going on inside. There are millions of dancing atoms in there. Everything in the world is made of dancing atoms."

And then he read her an article in Scientific American about atoms.

Sixteen years later, in 1926, when she was teaching design at UCLA and painting as a professional, she was asked by the chairman of the art department to hang an exhibit of still lifes and static dunescapes by photographer Edward Weston.

"What are you trying to do with these?" she asked the artist.

"Convey essence."

"If I ever get into photography," she told him, "it will have to move."

It was not as if, by this time, she was unaware of photography. A year earlier she had married Willard Morgan, a writer on the topic and a photographer himself. He had a darkroom set up in their bathroom, and Barbara Morgan recalls that "every time I went to the bathroom I got an education in photgraphy." Outside, he would position his 5-by-7 view camera and ask her to crawl under the black cloth and summon up her sense of design to adjust the bellows and ground glass. At first they focused on the buildings of Frank Lloyd Wright; later they took camera and tripod to museums to photograph paintings. She would say, "This isn't art; it's copying."

Every summer they would travel to the Southwest to study the rituals of the Hopis, Zunis and Navahos. Willard found that he could easily climb rock precipices with the revolutionary 35 mm Leica around his neck. He was able to take photographs from places where a bulky view camera couldn't be carried. The Leica company saw his work and invited him to move to New York and become their customer relations man. They moved east in 1930. In 1932, their first son, Douglas, was born.

"I found that I couldn't really paint anymore with a child around the house," Barbara Morgan says. "The daylight hours were filled, but I could work in the darkroom at night. So I took up photography. When I met Martha Graham, I had seen some of her dances and I told her that they were filled with rhythms that reminded me of the Indians. And she said, 'Indian rituals were one of the most profound experiences of my life.' Besides, I always felt guilty -- and she did too -- that my ancestors had taken so much from the Indians.

"I worked with her for six years. I had always been interested in oriental art. The Orientals say, if you want to paint a tiger, you have to become a tiger. I understood that a little, but I really learned what it meant in the years of working with Martha.

"All of the work was done around the schedule of the children. Lloyd was born in 1935. And the children always came first."

There's an old red printing press on the porch, half buried under fireplace logs. Her husband started a publishing company that her sons have kept up since his death in 1967. When they were children he would buy them old presses as toys. "Anything to widen their eyes," Barbara Morgan says.

Indeed, 40 years later, the place still seems like a haven for kids. The walls are covered with drawings that have been made by her grandchildren, and she has filled the rooms with objects they can play with, like Japanese temple bells and sand dollars and chambered nautiluses. There are also thousands of books covering every surface of the house: Joyce, Pound, Thomas Merton, Jeremy Rifkin's "Entropy," the classic works on symbolism by Cassirer. A National Geographic map of the world's ocean floors is pinned to a curtain. "I'm fascinated by the invisible," she says.

But she is also fascinated by the visible. She is an artist, after all, and only recently she has begun sifting through the thousands of negatives that have been neatly stored away in her studio. They range from snapshots of the children to documents of her travels among the Indians to scenes of New York in the '30s. And she is working an a new book, "The Dynamics of Composition."

"When I started working as a photographer, I thought it would be an interlude," she says. An impish smile fills her face.

And with that she is off in Petunia, racing down hills to run an errand, ever observant.