ELISSA MAKINIEMI Aalto is an agreeable, witty woman of sturdy build with hair the color of structural pieces of Alvar Aalto furniture. She is an architect, a good and an important one. You have to say that first. Then you can go on to mention she is the widow, as well as for many years the collaborator, of Alvar Aalto, the great Finnish architect (1898-1976).

Their office is known for warm and imaginative organic designs of houses, government buildings and hotels. But in the United States, Aalto's fame rests sturdily on his three-legged stools. Their blond, laminated legs, like tree trunks, hold up round, black seats, cupped gently in the middle, contoured to the shape of the human anatomy. The stools are great because they fit so well. But don't ever try to stand on one. The copy stools were designed in 1938.

His curving cantilevered chairs, often woven with black webbing (1946), and his whimsical cocktail trolley (1936) with its basket for bottles, tile for a work top and great disk wheels, are furniture classics.

You want to laugh when you see a piece of Aalto furniture. Not because it's silly-looking, although it has a quality of good humor. And it does look as though it were made of nursery-room blocks, assembled by some youthful paragon. The furniture is still made, and it is distributed in the United States through ICF of New York.

Now, three years after her husband's death, Elissa Aalto is carrying on the family business. "Our office still goes on," she said. "We have commissions for two churches, a city hall and a house, among other things.

"It's not so hard for me to continue the work, because I have always been in the office. I used to tease my husband, saying he was lazy - his first wife was an architect in his office, too." (Aino Marsio died in 1949.)

Elissa Aalto talked with officials of the American Institute of Architects and a few architectural buffs in the AIA executive dining room recently. She ate a fruit-stuffed pineapple with the relish of a person for whom taste applies to the tongue as well as the eye.

Aalto was in the United States for the opening of the splendid retrospective of her late husband's work showing at the Smithsonian's Cooper-Hewitt Museum in New York through Sept. 12. From there it will go on a countrywide tour. The exhibit was organized by the Aalto atelier with the Museum of Finnish Architecture.

Aalto acknowledged the difficulty in trying to carry on a famous architectural office after the great master is dead. "Of course, we try to work in the way he taught us," she said. "But he was always moving on, himself; trying new ways, doing things differently. And so we must as well. We can no longer ask him what to do. We must decide for ourselves.

"He never accepted the need for so many drawings. He was not like the architects today who have a drawing for everything. He would make changes as the building developed - don't you know that would upset everybody here, the contractor, the owner, everybody. But he regretted the need to formalize the plans because of costs."

Aalto still lives in the charming house her husband designed and built in 1934-36 in Helsinki. Nearby is their studio, built in 1955. The house has a fine roof terrace. Inside, a peg wall is a place to hang the architects' T-squares as well as their hats.

"The house has always been full of prototype furniture," Aalto said. "We always got the ones that didn't work." She turned serious. "Furniture was for him a part of architecture. He didn't separate types of design."

Later, walking through the exhibition at the Cooper-Hewitt, I saw the family resemblance among different sorts of structures - from table legs to pillars to ceilings. Goran Schildt writes in the catalogue:

"When he made his bent-wood furniture, he gave them first chair legs and table legs, but these soon became "little sisters of the column", as remarkable as the ancient marble columns from which the different building styles of antiquity evolved. In Aalto's architecture, too, the entirety grew from a detail loaded with deeper meaning. His third style of chair leg, shaped like a spreading fan, could become an entire church roof, as we see at Wolfsburg. In fact, nothing that Alvar Aalto built stopped at its actual function, at the task of creating a space or satisfying a practical need. There is always a humanistic added value, a heightened meaning."

Aalto is often compared with Frank Lloyd Wright. And indeed they share many preoccupations: love of wood and masonry - and wit. Most important was their common belief in organic architecture. Aalto was born in 1898, many years after Wright, who was born in 1867 and died in 1959. But both were an outgrowth of that tidal wave of inspiration most often called Art Nouveau, based on nature's forms, which washed away much of the tired eclecticism of the 19th century.

Unlike the Bauhausian architects, the organic architects didn't think there was anything sinful about curves. And undulations in buildings vases or people were no cause for distress. Their designs grew out of natural shapes.

Aalto wears jewelry designed for her by Alvar Aalto. You can see in the pieces the relation to his other work. "A day or two before a birthday he would hastily sketch something out and send it over to an old friend who was a goldsmith," she said.

Probably his most familar vase is the one he designed in 1937 for the Savoy Restaurant. It swells and ebbs like the water it holds. The shape is embossed on the catalogue cover. One of the displays in the exhibit showed the evolution of a bent-wood chair leg from wooden dowels gathered into a bundle, flattened and bent into a supporting shape. And beside the pieces are the tree truck that inspired it.

Aalto himself wrote that "architecture and its details are in some way all part of biology."

Aalto was a man who worried about every tiny detail. His door handles are like jewelry on the building. The handles for the Turun Sanoma (Turku, Finland) newpaper building (1928-30) and the Rautatalo commercial building (Helsinki, 1954) were obviously as important to him as the girders holding the roof up.

The structure was not neglected, though. The sunburst of wood supports radiating out from the beams in the Saynatsalo, Finland, town hall (1950-52) is nothing less than exuberant. That structure is a favorite of the Aaltos. She was the architect in charge of its building, and they were married there when it was finished.

All Aalto's buildings are rich in texture, wealthy in ornamentation. The structure is not ony revealed, but exalted. Most of all, Aalto's work, jewelry, furniture, buildings and life express optimisim, happiness and good cheer. The design wishes you well and helps you to be a part of a great and glorious natural design. CAPTION: Picture 1, three-legged stools of laminated wood; Picture 2, a bent-wood cocktail or tea trolley with basket drawer and tile top; Picture 3, a curving cantilevered chair with black webbing; Picture 4, the main building of the University of Technology at Otaniemi, Finland.; Photographs from Cooper-Hewitt Museum/Smithsonian Insitution Picture 5, Aalto in 1971; photo by Goran Schildt.; Picture 6, Inside Aalto-designed Institute of Pedagogics in Jyvaskyla, Finland.; Picture 7, Typical of Aalto furniture is this bent-wood scroll chair.; Photos from Cooper-Hewitt Museum/Smithsonian Institution