VALLT POSSONY, whose one-woman show of pottery opened yesterday at the Phillips Collection, was well known as a ceramicist here even before she became Joan Mondale's pottery teacher.

Possany looks as cheerful as a dandleion with her sunny face and the wisps of gray hair about her head. You might expect to find her making magic pots in a Sacher torte house in the Vienna Woods.

The allusion is not too far off. Possony was born in Vienna in 1905, studied there and was a part of the Osterreiches Werkbund, a craft group that was very influential between the wars. A soft Viennese accent still paprikas her speech.

She studies later in Armsterdam, lived in Berlin and Paris, leaving just before Hitler arrived.She and her husband arrived in New York with almost no possessions except for the two dogs her sister had left behind in their care. As they steamed in, each held up a dog to surprise the sister.

Possony is like that. The other day she should have had her mind on the coming show of her pottery at the Phillips Collection (through June 18) and a second opening June 25 at the Folger Library's Ann Hathaway Gallery. Instead she moped around the house terribly troubled because her huge cat (who would drink water only from the faucet) had just died at age 10 1/2. She lives with a great springer spaniel who, poor thing, wheezes most of the day, but still enjoys a hug from those who come to admire the potter's work.

Possony fell a while back and walks with great difficulty. "Up until then, the wheel I could still kick if I had to. But now, the electric wheel most of the time I use. The young people today don't want to bother to learn the hard way of the kickwheek. It's more work, but you have much more control," she says.

Possony's house nearby in Virginia is just the chocolate color of a Sacher torte. The building started out years ago as a barn, but really looks like a potting shed left too long under the grow-bulb. The front door latch sets the style for the inside. More than a latch, it's a wooden art work - hand carved, not ornately, but with a plain strength of character that says firmly: "I am the latch, and I work.%

The road to the house is hidden. Driving up its winding way, you feel something strange and wonderful must be at the end. Then, suddenly, there is the house, tucked under the great trees in a circle of violets and dandelions. It seems reasonable that if you broke off a bit of the house, it would taste sweet. Once inside the door, Possony, in the Veinnese manner, presses upon you coffee, tea, wine.

The first things you notice are the great semicircular, raised concrete fireplace and the kitchen that curves around from it. The kitchen's wall is a dark hardwood scren, ending just above the line of sight from the living room. Inside, there is a great oak counter, a semicircle like the wall. There's even a built-in wooden niche for the refrigerator, a problem since refrigerators back then were much smaller. The latch, the fireplace and the kitchen were all built by Wharton Esherick, the late famous woodworker, whose own house in Paoli, Pa., is a museum.

The furnishings for Possony's house - great sturdy tables and benches, early modern chair, desk and sofa - were all made by another good woodcraftsman, curtis Johnson, a pottery student of hers.

Today, just before her show opens, every surface that's flat, and some that are not, is covered with teapots, cream pitchers, wine pitcher ("It is such a nice pitcher, it should always have wine in it"), small dishes, large platters, bowls, compotes and some basic pots. Some 45 groups (a soup tureen with six bowls counts as one) will be in the Phillips show.

Most of the teapots have neat straw handles, so you won't burn your fingers. The pots feel right in the hand, balanced and full of body and texture.

"I don't have a thing I ever made that was not for a purpose. It's all meant to be eaten or drunk from. We don't have so much room in our houses anymore - we don't need things that aren't useful. I am for the simple-as-possible. The lid shouldn't fall out of the pot. The spout shouldn't drip (I hope this one doesn't). It shouldn't leak. in a pot for flowers, the hole should be big enough so the flowers don't have to stand straight up. These modern pots with the tiny hole at the top, not good. handles should be big enough so you can put your fingers in. You have to take care of pots. Here we have had people pour boiling water into cold cups, and they cracked, of course."

Her pottery's colors are appropriate to her bower, nothing garish or startling - the dark brown of rich soil, the gray of a rain-filled sky, the black of coal, the red and rust of clays. Her glazes are few. To vary the effects, she uses both oxidation and reduction-fired kilns. The reduction kiln is in a new building, finished last fall for her by Johnson, and powered by propane gas ($80 a tank), which burns the oxygen and makes smoke. The electric kilns inside her potting studio cook the pottery with oxygen without smoke. Possony, potters agree, is a master at judging the differing effects on the glaze.

"It takes many years to learn. Everyone who says different is wrong. Glaze I think is not so important now, the body is strong." Possony says.

"Now, if I am really working, I can make 50 pots in one day. But that is the least of the work. The hardest part is the finishing, the firing, the right glaze.

"To fire the kiln is the big thing. I load it. I kneel in it. I need two or three people to hand me the pots. Everyone loads a kiln differently. Everything affects the pot - what clay, what oxide, what glaze, where it is in the kiln, if upper or lower, if God is with you - no, leave God out - if luck is with you. On one firing, half of the load was brokwn. The pots, they talk to each other in different languages. I did not understand them."

The pottery is made in a big room with wooden benches, 12 electric wheels and two electric kilns. Three days of the week, Possony teaches classes. She has about 38 students now - down considerably from a few years ago. "I don't take everybody," says Possony. "I take only nice people. I think I can feel if they are nice. i have to be so careful so everyone in the class should get along."

Possony loves to teach. She took up teaching again in the United States at Walter Reed, working as a volunteer with injured veterans of the Korean War. After she was divorced from her second husband, she returned to teaching professionally. "I am a very good teacher, I think. Even if I should make my living from making and selling pots, to teach would still be for me necessary. Also I most do my own work, not just to teach. Otherwise you go stale." (Her only child, Andrea Ross, is a Prince George's County music teacher. Ross has two children and 400 students.)

Possony first taught in Vienna. She remembers to this day the first person she saw making a pot. "It was at the world's fair in Frankfurt. I was 3 years old. I remember seeing a great big black man making the clay spring up. I was fiscinated. When I was 18, everything was going on in Veinna. I saw a great exhibit in the Secession Haus, I knew I wanted to work at this.

"Vienna was a wonderful place then. We had everything, fasching balls, flowers, mountains, operas, theaters. I think the young people don't have so much. My father was a lumberman. When he was young he was very poor. I don't know how he prospered so. Even so it was always important to him what was eaten and how it was prepared."

Even today, Possony likes to bake bread. "When I am unhappy, I always make bread. it's very good for the nerves." For the Phillips opening, her students have divided themselves into two groups: those who bring cheese and those who bake bread. Among those promising homemade bread is Joan Mondale.

Possonycalls her a very good student. "Oh! She is so well organized. Never forgets to come. Always tells you if she is going to be away. She's never late. Hard she always works. When she comes here she is always so excited about pottery.

"I think she has done much good for craftsmen. She deserves much thanks. Today crafts are very big. The machine people have tired of."

Mondale has bought nine pieces of Possony's pottery for the vice president's residence. When she visited Mexico in 1978, she presented a Possony pot to the President's wife as a figt of the U.S. government. Many people consider it more appropriate for the U.S. government to honor American crafts by giving them to foreign governments on official occasions, rather than some mass-marketed object, as has been the tradition.

Everytime, it seems, that Mondale has talked about her pottery, she's included praise for Possony. In the foreword to the Phillips catalogue of Possony's show, she wrote:

"Vally Possony is a potter's potter. I say this because those who have worked with clay will instantly recognize the discipline in her work. Possony rejects the easy, the trivialM the instantly attractive solution which first seduces then fatigues the eye with extraneous ornament and superfluous color. In Vally Possony's work nothing needs to be added or taken away - the forms are basic and simple, the glazes are rich and sensuous. Both forms and glazes work together in equal partnership to create works of art which grow lovelier the more they are used and looked at. This is the consummate art of the master."