Fragile, blond Sally Poncet, eldest daughter of a dentist in Tasmania, is no ordinary woman. But then, her French husband, Jerome, and their three sons are not a conventional family, either.

Until recently, the Poncets lived aboard the 50-foot vessel that Jerome Poncet built in France in 1975. For months at a time, they had only each other for companions, along with scientists they met at research stations in the Antarctic.

Along with viewing some of the world's most starkly beautiful landscapes, they have also crossed beaches so crowded that they carried sticks to defend themselves against aggressive animals.

"Down there on a beach like that, there's one thing eating another," said Sally Poncet, in town on a rare visit to the United States to check in at National Geographic. "They're very matter of fact about life and death, the children."

This week, "Antarctic Adventure," a presentation of National Geographic Explorer (Sunday at 9 on TBS), follows them to the last unexplored continent.

The story began when Jerome Poncet, then 17, decided to build a yacht. In 1969, he left France on a 'round-the-world trip with friend Gerard Janichon. The boat called briefly at Hobart, Tasmania, where Poncet met Sally, a university student who shared his sense of adventure.

In 1973, Poncet and Janichon's yacht was the first to sail into Antarctica. After the men had returned to France in 1974, Sally and Jerome Poncet were married and the two men set out to build a pair of steel-hulled boats.

"When we first started, that was all we had, just the boat, and not much money at all," she recalled. But there was plenty of adventure ahead. She and Jerome would be ice-locked onto South Georgia Island in the Antarctic, the two of them would spend three months hauling a sledge around the ice, and their first son would barely survive his birth far from any helping hand other than his father's.

In 1976, the Poncets sailed for the Antarctic with plans to spend a winter. The couple was so determined that they would not be bothered by outsiders that they hadn't even bought a two-way radio. In the Antarctic, she said, "there wasn't much point anyway, because there was no one to come. But really we didn't want any interference. The project was important."

"The project" would become a series of surveys of the birds and animals of the Antarctic, resulting in statistics for international counts and articles for various magazines, including National Geographic (March 1989); a booklet for yachtsmen planning to visit the continent, and eventually, the Geographic film.

"All of '78, we were on the Antarctic peninsula, and we put the boat on shore and all the seawater froze," said Sally. "We got out skis and a tent and we spent three months away from the boat, just walking around the area where we'd put the boat up."

That year, Sally Poncet became pregnant. She and Jerome decided their child would be born at 106-mile-long South Georgia Island, claimed for Britain in 1775 by Capt. James Cook.

"I wasn't worried {about not being near medical aid}," she said. "It was a pretty easy decision to make, probably because there weren't parents or in-laws around. We were both very positive about it."

But at the end of winter 1979, their first child, Dion, arrived, a breech birth. His father, who had had first-aid training, saved him with mouth-to-mouth resuscitation.

"But there wasn't any way we would have considered going near a hospital or a doctor," said Sally. "In a way, it was a logical conclusion to our year down there. You do things in a certain way because of the whole year that had gone before."

The Poncets had been trying to get their trapped yacht out of the frozen sea since December 1978. At the end of February, a British ice breaker arrived to smash through the heavy ice and Damien II sailed out behind it. After the winter, the boat needed repairs and refitting, so the family went to Tasmania, Sally's home, stopping first at the Falklands.

Leiv was born in Tasmania in 1981, and two years later the Poncets sailed back to the Falklands and decided to make it their home of record. Lars Nigel (called Diti after the boat) was born in the Falklands in 1984. Three years ago, they arranged to share a lease to a 12,000-acre, four-island sheep farm. When the farm manager retired shortly afterward, the Poncets inherited the care of 2,300 sheep.

The Poncets have sailed to the Antarctic aboard Damien II to conduct annual bird surveys, sometimes with scientists aboard, each year since the '82-'83 season except for 1984, when Diti was born. In the early years, they also worked with the British Antarctic Survey to count elephant seals in South Georgia (there are about 360,000). This year they will count some 1 million fur seals.

Sally Poncet said over the years they have seen change, increasing recently because the Antarctic Treaty could be challenged for the first time in 1991 by any of 14 member nations. Some want to exploit mineral resources; others want to make it an international park.

"There's been frenetic activity," she said. "On one island at the tip of the Antarctic peninsula, there are 11 countries with a base. Even on Marguerite Bay, which is the farthest south you can get with a boat, the British are building a big air strip. That place will never be the same again. There's one hotel in the South Shetlands at the tip of the Antarctic peninsula, which has been put up by the Chileans. People are worried about the impact that will have on the environment.

"This year, it was sad in a way because it was like looking at the end."

There's been change for the Poncets, as well. Living in the Falklands has given them a sense of community, and now Damien II has a two-way radio. In June, Sally said, Jerome was alone on the boat when he had to call for help to get it towed off the rocks. "That could have been nasty," she said. "We've got really good neighbors and everyone was listening on the radio.

"Antarctica is different. You go down there, you have to realize that if you get into trouble you have to get yourself out of it. You've got to realize that everything you do down there is your own responsibility."

Life on the boat, she admits, has not always been easy for the Poncets or their sons. "At the end of the six months we've really got very little fresh stuff left ... potatoes, onions, apples and things. We drink powdered milk. In South Georgia, there's plenty of dandelions for fresh greens. I used to bottle {preserve} a lot of things, mainly meat and vegetables."

The boys often get seasick during the five-day trip to the Antarctic, and space is so limited that when National Geographic suggested a film crew, she was reluctant.

"There have been up to nine of us aboard, and it's okay if you go down for a specific job -- a bird survey, for instance -- and you put a lot into it for a short period of time. You don't think about it because there's a job to do. But I couldn't imagine going south with a film crew," she said.

And life is changing for the boys. In the Falklands, a teacher arrives for two weeks of concentrated instruction, then goes on to the next isolated family. Between visits, the parents supervise their studies. But for Dion, 11, a decision must soon be made: whether to send him to England or Tasmania for further education or to a boarding school in the capital, Stanley.

Sally, who taught them aboard Damien II, said the boys spend much of their time on the yacht drawing, inventing machinery, planning cities. They are fascinated by planes, having seen Chinooks and Harriers in the Falklands and others that fly in with their mail.

And they look forward to port visits that might include interesting people.

"The first years when we were going south every summer, they didn't go to school and they didn't have a lot of regular contact with children," she said. "Their main friends were the people we saw on the stations. We spend a lot of time with these people, who also had a lot of time and attention for them. These people really sat down and chatted with them. That was very important, as part of their education. Adults showed them the work they were doing and explained it to them on a one-to-one and equal basis."

Sometimes Sally thinks about the things her sons don't have -- "good music lessons, gymnastics or bicycle races, club sports" -- but like modern children elsewhere, they do have a videocassette recorder at home in the Falklands.

"I never thought we'd buy one," smiled Sally Poncet. "They started watching television at one of the scientific bases in South Georgia. The British had really excellent BBC wildlife documentaries. So we thought it would be a good idea to get a VCR and get good films. Dion is really keen on planes and aviation. We've got one on the Titanic. But Diti will watch cartoons if he can get hold of them."