Brother Benedict never really had a passion for teeth as a boy. He sort of fell into dentistry through his Navy career, but as it turns out he thinks it may come in handy to him as a Trappist monk.

The thing is that Brother Benedict left dental school a neat quarter-century ago - he was vice president of his class at the time - to become a monk. Just up and quit at Christmas vacation. Even since, he has felt this was a loose end in his life. His monastery gave him permission to return to Georgetown to finish school, and at long last he graduates today.

This spring his old class held their 25th reunion and people were amazed to see Brother Benedict still attending classes on crowns and bridges.

Rome was not built in a day.

"They didn't judge me," the monke said of his reuniting classmates after they had all returned to their far-flung water-drippers, "but I could tell they all thought I should have finished 25 years ago."

Still, unless dentistis lead more thrilling lives than most people, Brother Benedict can hardly regret not being a dentist. He chose, instead, a life isolated from common concerns.

Trappist monasteries are usually situated far from hubbub - his is in Colorado near a great protected wildneress out from Aspen. For most of his years there Brother Benedict and the other monks observed the Rule of Silence. No conversation occurred, except with his abbot superior from time to time, and on rare occasions of family visits.

"If my family came to see me, I would think of it later - how astonishing it was to hear their voices."

In an age of interminable chatter - the Republic may some day talk itself to death, one sometimes thinks - the austere monks never even said hello.

"We used our voices a lot, though. There are Gregorian chants in the chapel at intervals through the day, and at meals someone read aloud to us."

After Vatican II the rule was relaxed, though most people who have interviewed Trappist monks will verify they never learn volubility or garrulousness.

"When the rule was relaxed it was delight to me," the monk said, "but I think we may have also lost something at a profound level, while we gained something in communication."

In the years nobody spoke, Brother said, there was plenty of nonverbal communication. "You could always tell," he said, "if a monk knock things around or slammed doors."

It was a clue.

Here at Georgetown University finishing school, the monk has been surrounded by a new generation.

"Fantastic," says Brother Benedict if you get him on the phone. He has learned to say that word which means, "sure." He has not yet learned to pepper his talk with "you know" and like that.

The shock was not so severe for him as it might have been for some Trappist monks, because for some years he has done chores for the monastery that threw him into the ordinary world, like selling 40,000 chicken eggs a week to the local groceries, mending several miles of barbed wire fences, running the cattle-breeding program, selling gifts at the monastery shop, and making sculpture an performing magic.

But to backtrack, he once was taken as a little boy to a Trappist monastery in New England. The seeming tranquility and dept of life there struck him, but he never thought much about it afterward.

He grew right along, as children do, in Pawtucket, R.I., and conceived Johnston a passion for baseball (he played semi-pro with the Pawtucket Indians as shortstop) and sports in general absorbed him. Golf, boxing, basketball - you name the sport and he like it.

Then World War II came along and he joined the Navy - his younger brother was a machine gunner who fought at Monte Cassino.

Monte Cassino, so badly damaged in the Italian campaign, is the great abbey founded by St. Benedict.

Brother Benedict does not wish to tell you much about the brother, who lives in Rhode Island. Suffice it to say Brother Benedict took the name of the founder of Monte Cassino and left behind his boyhood name of Joseph Harold Grant Jr.

Just after the war he had "a great interest in the priesthood," but it passed as youthful enthusiasms often doe, and he got caught up in magic tricks, dentistry and baseball. Unless he goes into a book-length biography, it is hard to explain it all, but he wound up in dental school at Georgetown.

Nobody forethought in those years he would be a monk. He was big in his class and girls liked him and he had no thought of a monastery."

He still cannot say what got into him one Christmas vacation, when he went hom to Pawtucket and decided to go visit the old monastery he had visited as a boy.

It happened quick.

"On that visit, they didn't even want me to come back from vacation. They thought I had waited too long already to become a monk, and I think maybe I did wait too long." Something had been going on in him he was not aware of. Working on the cadavers in anatomy classes he had thought a lot about death and eternity and the transience of things. The corpse of a young man especially got to him.

So there he was in the odd position of saying good-bye to the school where he was going great guns, and entering on a life apart from the world.

To bring him down to earth, perhaps, from his lofty-spirtual decision, the monastery set him to work "washing dishes, lugging rocks around, digging ditches and pushing concrete."

His vocation stuck. Luging rocks didn't turn him off.

After he had been a monk for a time, he "did a rope trick for the abbot," who was one of those men that nothing can surprise. The abbott was enchanted at Benedict's skill. Why not a magic show for all the monks, the abbot suggested.

Thus this monk became one of what must be a very small number however put on an hour-long magic show at a Trappis monastery, the audience silent as ghosts.

"They were from 18 to 90 years old," he says, "and they responsed very well." A performer cannot be fooled, and hardly need vocal huzzas when he has touched hearts, no matter what his medium may be.

The years that followed were happy ones. The main thing was his spiritual growth, his understanding of himself and his place in the scheme of creation.

Monks rise at 3:15 a.m. and enter the chapel. All through the day till night, in their ancient rhythm, they work, they read, they worship, they chant the immemorial offices of their faith.

But if spiritual development is a chief goal and all one's life is arranged to help one reach it, then more is expected, and falls are more painful.

"The loneliness was great," he says. "Especially on winter nights."

Sex was even more of a problem than he thought it would be. The voluntary giving up of a great gift was something he had worked out well in his theology, but it wasn't an easy accomplishment.

After a few years at the New England monastery he went to the new one in Colorado. He slept in a barn with the other monks, while they built the fine brick buildings from scratch, the arches finished with courses of moulded bricks, and other careful details.

He had the management of 2,000 calves. Seven or eight hours a day he rode the range. Now the monastery leases its range lands, but Brother Benedict still holds on to his cowboy hat. He worked on the harvest of 1,000 tons of hay, he repaired sled runners and farm machinery. He managed the breeding of the Herefords.

He shoed the horses and learned to forge iron. It is a delicate thing to fit a shoe to a horse. It better be right.

The monastery sent him to Kenneth Lynch in Connecticut, a famous iron artist, and there he learned yet more. He began to work nuts and bolts into iron sculptures.

He took a correspondence course in cartooning. He got interested in law, and would like to get a degree in that.

He found his sculpture sold. He had made 350 sculptures, 150 of them crucifixes, but cowboys and western scenes as well. One, easily confused with a Nativity scene, is an elaborate miniature blacksmith shop with the horses standing around.

Some he has sold to restaurants, some to individuals including Robert Mann, violinist with the Juilliard Quartet (who hopes to be at the graduation today) and Wayne King, the band leader. But the blacksmith shop has a price of 5,000 on it, because he hopes that is high enough that nobody will buy it.

He is chapter chairman of Cloistered Artists Guild of America. "Monks and jailbirds," he says, and other artists who lead sequestered lives, are in that group.

In Washington he has been living with a family off Foxhall Road while finishing school. They have beautiful kids and it's a lively bright place, with a lot of noise.

Recently, he spent a weekend on a farm to help out.

Things went wrong. First he get a flat tire at Purcellville, Va., possibly no worse than anywhere else, but it was a drag. Franciscan priest in his robes helped him with the tire. (The jack, of course, did not work). Then he ate something and was sick a couple of days.

The question came up - he is an expert, after all - how a person changes for the better. Say he wants to straighten up and fly right. Should he read the riot act to himself, or shame himself into improvement, or what?

Brother Benedict doubts severity works. In his own case, it did not good to reproach himself. Anxiety and agony was never reckoned virtues and almost always get in the way.

Love works, he thinks, It's positive. Love is not dwelling on itself, or thinking of mistakes or evils. It is not thinking of itself at all but something outside the self. Sometimes, Benedict suspects, it is best to let a fault ride, if the alternative is an obsession with it.

"We are all too likely to allow it to get into our consciousness - instead of letting the roots of it dry up in the sun. The great thing is being ourselves in peace. Even worrying about it ever being done is a hindrance. Some of the greatest saints were great because they - because of their faults."

It made the tension that propelled them into higher planes.

Rome was not built in a day.

"There can be a fear of not being thought good, and that id destructive," he says. Because goodness is not a con game to be played for scores.

He wonders if people will think he is nuts and would be embarrassed (he says) "if they came and started feeding me bananas."

For himself, he is pretty sure, "understanding is all."