LIKE MANY great craftsmen, Albert Kumin is sometimes at a loss for words, particularly when it comes to talking about himself.

"I had quite a hand for it," the White House pastry chef conceded about his apprenticeship in Switzerland during the days before World War II. "And I was lucky. I always had good chefs to work with."

The pastry man's craft has changed dramatically during the 42 years Albert Kumin has been practicing it. That he has changed with it, and has been a major innovator and teacher, are enough to set him apart. But those who know him well won't settle for a whipped cream rosette or two.

They demand a piece montee .

"He is the ultimate pastry chef of his time," said Joseph Baum, who brought Kumin to New York in the late 1950s to open The Four Seasons and called on him again nearly 20 years later when planning the spectacular food complex at the World Trade Center and its showcase, Windows on the World. "He has taken a creative and precise art and transposed it to the large scale necessary today. He is not just an architect or decorator. He has the blessing of taste."

"I've never seen any man so constantly interested in sharing his knowledge with young people," added a colleague from Kumin's days as a teacher at the Culinary Institute of America.

The object of this praise, echoed even by his rivals, stands in the White House kitchen, his fresh white uniform already marked with streaks of chocolate, and the base of his ancient white toque discolored from long hours of hot work. Turning to help Amy Carter locate some coloring for Easter eggs, he is friendly, polite, even deferential in the Old World way.

Everything but the politeness falls away as he works. The pastry chef's mentality is quite different from that of the sauce chef and few have the talent to excel in both disciplines. The saucier is impetuous. He works within limitations, but chemistry has given him far more leeway than the baker. Last minute improvisation can correct or mask mistakes. But most of the baker's failures are terminal, so he plods along precisely, time after time, to the point where his fancy can take flight. Albert Kumin doesn't count eggs for a recipe, he measures them. He weighs flour, sugar and butter, not trusting "spoons and cups and all that stuff" for large-scale production. Small inaccuracies can add up rapidly.

His hands, scarred from countless encounters with boiling hot sugar, are large, each finger a calloused peninsula. Yet his movements are astonishingly deft and he works so fast there isn't time to observe his technique. Sugar so hot an ordinary mortal would drop it and yelp with pain is cut and bent into graceful flower petals. Cookies are formed so precisely they are indistinguishable one from another. Dough is shaped as though it were on a potter's wheel. It doesn't stop there. Melted chocolate is formed into a beautiful round box in less than 15 minutes. A woven gold basket with a spray of flowers tied to the handle emerges, pulled from lengths of molten sugar. His chocolate rabbits are so finely etched that the candy looks like fur. Kumin is the John Henry of his trade. You would pit him against a machine any day.

"In my time," he recalled of his early days, "there was no time. If your chef needed you, you worked-12 hours, 14 hours, 18 hours. And you did some fancy things after. It was a challenge, a little bit your own pride that made you do it."

His mother's kitchen in the town of Wil, not far from the border with Austria and Germany, fascinated him. At age 15, when the time came for him to learn a trade, his parents thought it was logical for him to learn about something he liked. They were right.

"I never was sorry since," Kumin said. "You would go to work at 5 or 6 a.m., then go to school from 1 to 9:30 and maybe work more in the evening. If you did something wrong twice, you'd get a kick in the fanny.

"I'm not sure that system was more effective than the way they learn today. The times were different. You couldn't speak up. If you went home and complained, well, my father was quite a hefty guy, too."

When World War II arrived, he combined work and soldiering in various parts of Switzerland. Moving from job to job, he gradually assumed more authority. At 24 he was a pastry chef, but unlike today's young "chefs" he had compiled nearly nine years experience. "It was different then," he said. "Competition in our field was tough and there were many talented guys available. So after a time the chef would give you a push and say it was time to go work for somebody else. Here in the U.S., when they find someone with talent they try to hold on. The young people don't move about and they don't learn as much."

The nomad tradition was so strong that it was only natural for Kumin to think about working abroad once the war ended. Many of the best chefs he met had done so and told beguiling stories about their adventures. So in 1948 he arrived in Canada and joined the staff of Montreal's Ritz-Carlton.

Two hotels and 10 years later Joe Baum lured him to the United States.

"I didn't know what I was getting into," Kumin said.

No wonder. Baum was furiously building a chain of dining places for Restaurant Associates linked only by their innovative qualities and an unfettered ambition to set newstandards of excellence. The Tower Suite, the Brasserie, Forum of the Twelve Caesars, La Fonda del Sol, Zum-Zum: Kumin planned menus and developed pastries for them all. But it began with The Four Seasons.

"Mr. Baum was a very hard man to please," Kumin acknowledged. "He wanted something special nobody had or to take something old and devise something new from it. At times I thought 'can I ever please him right?' I went to the World Trade Center two years before we opened, I can't count how many times - until the lemon torte or the truffle cake were what a majority thought the public would be really crazy about. I think a lot of it is taste. I am very fussy about the difference between good, very good and delicious.

"They needed someone who was willing to accept the criticism. But it helped me, too. If I'd been with an ordinary man, easy to please, I wouldn't be where I am today."

In 1972, Kumin went to the Culinary Institute of America at Hyde Park. "The kids loved him from the frst day he showed his face," said his wife with pride. When he moved on to the World Trade Center, he made it a post-graduate school for promising young bakers from the C.I.A.

He was on the verge of returning to Hyde Park when the White House offer was made: "I thought to myself it's the only job of its kind," Kumin said. "There are lots of hotels, but only one White House, and you're the only asked once."

But in the midst of what Baum called "icing on the cake" of his career, Kumin continues to think about the young. On Friday he was back at Hyde Park, making a speech to a class of C.I.A. graduates. They and their contemporaries, he feels, "are as good as anybody else.

"It's a hard life," he said. "But I think young people are very, very interested in our field. I encourage them and I push them a little at the World Trade Center. You wait a few years. They will be in competition with anyone in our field. All they need is a chance to prove themselves." CAPTION: Picture 1, White House pastry chef Albert Kumin, his chocolate Easter bunny, by Harry Naltchayan-The Washington Post; Picture 2, no caption; Picture 3, Albert Kumin in the White House kitchen, by Harry Naltchayan