Lennette Warren, a senior from Bladensburg High School in Prince George's County, sat in on the National Zoo's slide show about Golden Lion tamarins yesterday, expecting a serious lecture that would put her to sleep.

But that was before primatologist Benjamin Beck started talking about teaching monkeys to peel bananas.

"We'd show them a banana, and they'd just sniff it and walk away," said Beck, discussing a recent, successful project aimed at "re-introducing" captive tamarins, or tiny monkeys, to the forests of Brazil. "They only knew about bananas that come cut up in small pieces. They didn't know about whole bananas."

Beck's account of the trials and tribulations of preparing the zoo-bred monkeys for a wild habitat captivated Warren, 17, and nearly 300 other area high school students and teachers who attended yesterday's natural science symposium. Zoo officials put together the program -- the first of its kind -- in hopes of attracting more teen-agers to the the zoo and interesting them in careers in animal research and conservation.

"We're raising horizons about what the devil goes on here," said zoo spokesman Robert Hoage, noting that attendance surveys indicate that not many teen-agers visit the zoo.

The two-day symposium, which concludes today with a tour of zoo exhibits and a chance to watch an elephant-training demonstration, spent yesterday apprising the high schoolers that a lot more goes on at the zoo than the mating of its celebrated giant pandas.

Pathologist Richard Montali, the zoo's "Quincy," told how he was summoned from home one Saturday two years ago when the zoo's ducks started dying off. The culprit: botulism from fly eggs and sediment in the pond. The keepers and veterinarians washed out a lot of duck stomachs that weekend and saved most of the flock.

Zoo professionals have to be on guard for "zoonoses," diseases transmitted from animals to humans, Montali said. And they need to know about a range of common and exotic vaccines, because zoo animals do not always respond to vaccines prepared for domestic pets.

How do you keep the animals from getting bored? Edwin Gould, curator of the zoo's mammals, suggests hiding raisins in the hay for the gorillas to find. Or installing play structures. Or varying feeding schedules.

At the "Sex at the Zoo" discussion group, David Wildt, an animal reproductive physiologist, said the "new zoo" relies as much on people in white lab coats as it does personnel in the field. While students peered at mice embryos or buffalo sperm cells under a microscope, he and other researchers explained the latest techniques for helping animals to breed.

"You just don't take sperm and put it in an animal and expect it to get babies," Wildt cautioned, noting that a lot of research is necessary before artificial insemination and embryo transfer is successful.

That was pretty much the story, too, for the Golden Lion tamarin project, according to Beck.

"Zoo animals are fat, lazy, urban beasts," said Beck, describing the problems of trying to teach captive monkeys to survive in a special reserve in Brazil.

"Some of these guys would get out in the boonies and they'd just give up," he said. "We'd have to walk them back (to their cages)."

Zoo workers spent months teaching the monkeys to search for food, installing and rearranging natural vegetation in the cages and allowing them to learn from their mistakes.

"They'd try to eat a bee, and a little thumb would swell up," Beck said. But the monkeys never tried to eat bees again, he added, and most of those finally released into the reserve, especially the youngest tamarins, survived and are breeding.