They're not just a pretty face: they're a scientific wonder

What swims like Esther Williams, walks like Charlie Chaplin, dresses like a maitre d', and until recently was a featured attraction on menus in southern Chile?

For all the fun and folklore that surround penguins, scientists say there is much to learn about these dapper birds - particularly how it is that they know more about the weather than does the 6 o'clock news. Because many species are dying out, special penguin environments are being constructed in California, Maryland, New York, and Scotland to keep the birds alive while studying them under controlled conditions.

In 1982 the first captive-bred emperor penguin was hatched and raised at the Hubbs-Sea World Polar Research Institute in San Diego. And just last week the world's newest and most sophisticated penguin environment, at San Francisco's Steinhart Aquarium, had its first captive-bred penguin hatch.

''We're trying to educate the public while we save a few penguins' lives,'' says John McCosker, a self-styled ''penguin historian'' and director of the Steinhart, which has just become home to a colony of rare and endangered black-footed penguins from off the South African coast. ''Their normal population of tens of millions has been reduced to tens of thousands,'' Mr. McCosker says.

The hunting of penguins and their eggs for commercial purposes has been illegal since the passage of the Antarctic Treaty of 1959. Recently, however, the Japanese have petitioned Argentina to harvest the Magellanic penguins for high-protein livestock food. Subsequently a prominent American penguinologist, Dee Boersma, flew to Patagonia to study the species' reproductive habits in hopes of coming up with a conservation policy.

Other species face different man-made threat: oil spills. Because penguins tend to cluster, a major spill can destroy entire species. The black-footed are especially vulnerable because they live perilously close to the oil shipment route around Cape Horn.

McCosker says a recent oil spill threatened to eliminate the black-footed species. But the wind shifted, he said, and the majority of the penguins were spared.

Extraordinary as it may seem, one species of penguin may be able to tell scientists how to predict the time of El Nino, the atypical weather pattern that last year brought droughts to Australia, typhoons to Tahiti, and torrential rains to California.

El Nino's visits take most human beings by surprise, but the diminutive Galapagos penguins, which live on the equatorial islands off Ecuador, know just what hit them.

''When certain signs are present, the penguins know El Nino is coming and maximize their strategy for survival,'' McCosker says. Under normal conditions, penguins breed, then molt annually. In El Nino years, however, when the food supplies decrease, the Galapagos penguins skip breeding in the season beforehand so that they will have the energy to molt, something they must do to survive.

''A lot of nature's indicators are too subtle for us to identify,'' McCosker explains. ''But birds have done it for millions of years. They know something we don't know. We should listen to them.''

Penguins are especially sensitive to temperature and other environmental conditions and may one day monitor pollution levels, much as caged canaries were used to monitor deadly gases in coal mines. Once scientists know more about them , penguins might act as barometers of wilderness management, says Scott Dreischman, curator of birds at San Diego's Sea World. ''Monitoring the reproductive level and overall health of the antarctic penguins, for example, can help scientists determine whether or not man's presence is harmful to the environment,'' he says.

Inhabiting only the Southern Hemisphere, penguins, contrary to the stereotype , generally like it hot - or least warm. ''Of the 17 recognized species, only two live on the polar ice,'' says Christina Slager, one of the biologists who planned, built, and maintain the Steinhart environment. The other species are distributed along the fertile currents that spread north from the Antarctic to the equator.

Penguins have adapted to climates ranging from 107 degrees F. (near the equator) to -80 degrees F. (in the Antarctic). They have a high metabolic rate and are so well insulated that they are often more concerned with cooling off than warming up. Warm-water species are equipped with bald spots to keep them cool. Others just ruffle their feathers or go for a dip when temperatures rise.

Western man's first close encounter with penguins came in 1519, when they were sighted by one Antonio Pigafitta, a tourist-class passenger on Magellan's trip around the world. Soon thereafter, they became breakfast, lunch, and dinner for the early explorers. As recently as 20 years ago, their eggs were still listed on menus in restaurants along the Strait of Magellan.

Although the first interest in penguins was culinary, scientists have since taken a scholarly interest in their evolution. Fossils over 70 million years old suggest that the birds were once airborne. Their wings - which were of little use in gathering food - gradually became smaller so they could be used as flippers; their bodies became elongated and streamlined so they could ''fly'' through the water.

Their feathers increased in density - over 70 per square inch - to fit them with watertight, well-insulated ''wet suits.''

Today, what scientists know most about penguins is their mating habits.

''Ninety percent of our knowledge covers 25 percent of their life - breeding, '' says Mr. Dreischman. Penguins choose a mate when young and usually stay together for life. One researcher estimated the penguin divorce rate at a mere 17 percent.

Courting males, scientists report, engage in ''ecstatic displays'' to attract single females and to keep other males off their turf. Once the male has attracted the interest of a potential mate, he struts away without a second look. If the female is interested, she follows. An amorous Adelie male often presents his intended with a carefully chosen pebble, the stuff of which penguin nests are made.

If the prenuptials smack slightly of male chauvinism, family-rearing does not. Once the egg has been laid, the female takes off to feed, leaving the expectant father at home to incubate the egg.

There is no need for the male to feel smug about his role in bringing up baby , however. At San Diego's Sea World, scientists have discovered that even the father may be expendable. ''E. P.,'' the world's first Emperor penguin chick born outside the Antarctic, was hatched and fledged under the watchful eye of a warm stuffed dog.