Zoos are great places. Where else in our crowded urban landscape can we see and learn about wildlife, briefly escape the sights and sounds of the city and introduce our children to wild animals face to face?

If zoos did not exist, we would have to invent them.

Public awareness of the role of zoos in wildlife conservation and the desire to see animals in authentic settings are on the upswing: "A zoo is a means to an end, not an end in itself," says Michael Sands, a Boston architect and designer of zoo exhibits.

Most zoos have replaced sterile cages with large, natural enclosures that suggest an animal's native habitat, and zoos have become breeding centers for many species now rare or extinct in the wild. Perhaps even more important, zoos have become our link to a natural world.

"City people don't see live animals other than dogs and cats or rats and pigeons," says Michael Robinson, director of Washington's National Zoo. "People should go away from a visit to the zoo with an appreciation of how complex, diverse and endangered wild animals are: That is the responsibility of zoos."

Facilities as diverse as the Bronx Zoo, the Metro Zoo in Miami, the Woodland Park Zoo in Seattle and the North Carolina Zoo in Ashboro have recreated African plains. None, however, have done so on a grander scale than the San Diego Wild Animal Park, an 1,800-acre extension of the San Diego Zoo 30 miles north of the city. Herds of zebra, wildebeest, giraffes, elands and gazelles mingle freely, much as they do in the wild. Nearby -- separated by hidden barriers -- are lions and cheetahs, their natural predators.

Meanwhile, the Bronx Zoo has crafted a South American pampas whose dwellers include rheas (large flightless birds), peccaries (piglike animals), guanacos (a camel-like relative of the llama) and cavies (burrowing rodents that look like jackrabbits but are really large guinea pigs).

The Minnesota Zoo, 20 minutes south of Minneapolis-St. Paul, has created an unusual "Northern trail" exhibit focusing on animals and settings from the world's northlands. Visitors view wildlife that live in climates similar to that of Minnesota.

In the winter, the snow-encrusted forest exhibit is home for the zoo's 17 Siberian tigers, the world's largest cat. Herds of pronghorn, elk and American bison roam near the burrows of a prairie dog town.

In contrast with such large outdoor exhibits, many zoos have recreated tropical rain forests indoors. Chicago's Brookfield Zoo, for example, houses some 20 species of animals and thousands of plants from West Africa in an area the size of 1 1/2 football fields.

At the San Diego Wild Animal Park, a 10-acre exhibit brings an Australian rain forest to life. Koalas, kangaroos and wallabies abound. Rushing waterfalls and automatic sprinklers keep the humidity high.

Some zoos are noted for their one-of-a-kind exhibits or for specializing in certain animals. Who would go to the National Zoo without seeing the giant pandas, or visit Chicago's Lincoln Park Zoo and miss the gorillas, chimpanzees and orangutans? Or bypass the Cincinnati Zoo's world of insects?

The Washington Park Zoo in Portland, famous for its elephants, has built a far-ranging education, research and conservation program around the beasts. It is the only U.S. zoo to successfully breed Asiatic elephants.

Many zoos feature "zoo labs," where a crocodile's leathery skin can be touched, or a hippo's skull examined. Some zoos, like Minnesota's, let you hold or touch live animals, from silky exotic rabbits to squishy sea anemones.

Kids can don oversized plastic ears at the Bronx Zoo to learn what it is like to be a fennec, a small Middle Eastern fox. Or they can sit in a manmade bird nest, crawl through a make-believe prairie dog burrow, slide lizard style down a hollow tree or climb thick ropes shaped like a spider's web.

"The increased professionalism of zoos means animals are surviving longer," says Theodore Reed, a veterinarian and retired director of the National Zoo. "We have more trained, dedicated brain power to apply to the welfare of animals than before."

Zoos also are devoting increasing time and money to scientific research both in captivity and the wild. "Zoos must -- and have -- become producers and not just consumers of animals," says Edward Kohn, former director of the Minnesota Zoo.

The National Zoo's conservation and research center is in Front Royal, Va., an hour's drive from Washington. The Bronx Zoo operates a research and breeding facility on St. Catherine's Island off the Georgia coast. At the San Diego Zoo, scientists are developing a frozen sperm bank to store semen from zoo animals. The Minnesota Zoo houses a computer-based dating system that tells curators and keepers around the country the name, age, sex, location, parentage and health of more than 50,000 animals.

The American Association of Zoological Parks and Aquariums (AAZPA) has set up species survival plans that coordinate the work of zoos in saving endangered animals. 37 species have been included in AAZPA plans. They range from powerful cheetahs, Asiatic lions and Siberian tigers to the prehistoric-looking Indian rhino and the beautiful golden lion tamarin, a tiny South American monkey whose wild population numbers only a few hundred.

Nevertheless, problems remain. For one, despite success breeding animals in captivity, zoos can probably save no more than a few dozen endangered species. They cannot protect whole ecosystems, such as the Amazonian rain forest, with its complex web of animal, plant and microbe life. At best, zoos can rescue the large, glamorous and appealing animals.

The future for zoos? The National Zoo's Robinson thinks that the distinction between zoos and natural history museums will diminish. "Zoos," he says, "should function as a science teacher. We should put skeletons or models of animals next to live ones. It makes no sense to separate the two."

Robinson also would like zoos to develop ways to exhibit -- and thus preserve -- whole ecosystems. He suggests that indoor botanical gardens might feature live insects, spiders, frogs, small animals and other creatures running semi-free in their native vegetation. Or such animals might be put into existing botanical gardens.

Finally, Robinson sees computers expanding the concept of a "participatory zoo." Video games might be used to get wildlife conservation concepts across. Or computer programs could let kids compare, for example, their broad-jumping abilities to a kangaroo's, their speed with a cheetah's or their vision with a hawk's.