* Five King penguins strolling along a footpath in Switzerland's engaging zoo in Basel, their human escort trailing at a distance out of regard for their vast dignity.

* The Toronto Zoo's great tank enclosed by glass walls through which one peers, a nose away, at huge polar bears frolicking underwater.

* An Amazon jungle scene at the Bronx Zoo's World of Birds, where dazzling creatures streak about when they are not taking shelter from a simulated tropical downpour.

* The ''Exotarium'' at the Frankfurt Zoo, with such spectacular panoramic displays as a glass-enclosed replica of Antarctica, where penguins waddle on real ice.

For its size, probably no country is richer in zoos of quality than England. The traveler there can choose from a rich field, starting, for my part, with Whipsnade Park, some 30 miles from London.

Part of a complex managed by the Zoological Society of London, these 500 acres of what was once rolling farmland can be reached by car or a short train trip to Dunstable. Once there, you can drive or ride the ''Whipsnade and Unfolozi Railway.'' But it is best to walk because you will be almost as excited by the creatures on the loose as by those that are penned up - if anything can be considered ''penned up'' in a paddock as large as some entire metropolitan zoos. At any turn you may encounter a muntjac -a deer the size of a small dog with a bark to match - a pleasant and harmless prairie dog or a Patagonian cavy, or even a Chinese water deer with a wispy Fu Manchu mustache.

What makes the park remarkable is the combination of the restful rural vistas of Bedfordshire with one of the most sophisticated collections of wild animals in the world. Besides being a fine showplace, Whipsnade serves a double purpose. It backs up the London Zoo with a remarkably fertile breeding program, while at the same time relieving it of excess herd animals.

Whipsnade has supplied zoos around the world with cheetahs, which until 1960 were not bred in captivity at all because zoo people were still unaware of the inhibitions produced in that species of loners by any mingling of the sexes except, specifically, for sex. Other breeding successes, whose end results are likewise a pleasure to see, are white rhinos, Mongolian wild horses, Chilean flamingos, Manchurian cranes, musk oxen, polar bears, and pygmy hippos.

For something almost as out of the way in zoological centers, I would urge a visit to the town of Chester, some 18 miles out of Liverpool. A jewel in a fair setting, the Chester Zoo is a park in which the plant and animal kingdoms enhance each other. Not only are the pleasant gardens of England to be seen on every hand, changing with the seasons, but plants and flowers appropriate to the animals' various habitats are to be found even within their enclosures. The Tropical House, for reptiles, insects, and free-flying birds (chimpanzees and gorillas accommodated in rainy weather) is lush with palms, hibiscus, and bougainvillea. In the Elephant House, but beyond the reach of its tenants, are plants selected not only for decoration but for a fragrance that dilutes the bouquet otherwise noticeable in elephant houses.

In the tradition of ''zoos without bars'' - Chester was a pioneer - chimps and even rare Mountain gorillas are to be seen, at least in fair weather, on grassy islands separated from the public only by moats, the arrangement taking advantage of the primates' fear of water. The elephants, too, enjoy an island-like acre while free to retreat from a sometimes unkind climate to the greenery of their indoor quarters. ''If I were an elephant and were given my choice of where to live,'' an American zoo authority once observed, ''I'd go to Chester.''

The other ''must'' in England is the Wildlife Preservation Trust on the Channel island of Jersey, sometimes known as the Durrell Zoo, for Gerald Durrell, the great nature writer and its guiding spirit. The Trust is a haven and behavioral research center for small animals in danger of disappearing from the earth - for examples, the hutia, a Jamaican rodent, the big-eyed lemurs from Madagascar, and the waldrapp, a rare ibis with a curved beak and irridescent plumes.

No doubt some observers will be shocked, perhaps rightly, at the omission of their own favorites - Edinburgh, perhaps, or Marwell in Hampshire, or Bristol, or any of a dozen others. They can make good cases, particularly, I think, for Bristol, which is widely admired for the beauty of its gardens as well as a superior collection that includes the rare okapi and the white tiger.

Over as large a stretch as the Continent I will have to be even more stringently selective. For reasons perhaps best left to psychologists, zoos of the northern climes are more imaginative, more charged with concern and affection for wild creatures, than those of more southerly regions. I would propose three Continental zoos as basic, with several others to be seen if at all possible. The three are in Rotterdam, Frankfurt, and Basel.

Rotterdam's new Blijdorp Zoo had hardly gone into construction when World War II broke out. A single bomb so obliterated the justcompleted sea lions' pool that nothing was ever found of its inhabitants. But now a richly landscaped, selectively populated zoo, Blijdorp has succeeded in offsetting even the frequently wet Dutch weather. Its main area is a great sheltered structure, with reptiles and amphibians in the center, flanked on one side by quarters for the great apes and pachyderms and on the other by a bright walk-in aviary.

Aside from its superior layout, the zoo is notable for having bred enough orangutans to supply other zoos with specimens even after the species is gone from the wild, which threatens to be the case in the near future. Since the war Blijdorp has also produced so many tigers - Sumatran and Siberian as well as the more familiar Bengal -that while the species is dying out in nature, the zoo is obliged to put most of its own specimens on birth control pills.

To the east, few zoos can match Frankfurt's for a detailed concern with the needs, not to say desires, of their tenants. The sharp-eyed visitor will notice, for example, besides the usual variety of jungle-gym equipment for the apes and monkeys, numerous small touches that can make such a difference in their lives. Fresh green branches are supplied daily in order to counter boredom rather than for nourishment, each branch being good for protracted probing and chewing. As in many good zoos, currants or raisins are sometimes hidden in the straw floor-covering of enclosures to serve the same purpose. Similarly, I have seen young monkeys at Frankfurt enjoying, as much as human babies, the excitement of playing peekaboo by covering and uncovering their heads with paper bags provided for the pastime. Other such touches are the slide for playful otters and a degree of humidity in the aviaries that allows hummingbirds to bathe in the dew on the leaves.

In the Rhine city of Basel, where France, Germany and Switzerland meet, inhabitants talk fondly of their ''Zolli,'' or little zoo - short for Der Zoologische Garten. The diminutive is a measure of the well-deserved popularity of this physically minor but zoologically major establishment.

What the casual visitor sees at Basel is a green and pleasant park of a sparkling cleanliness that would be remarkable anywhere but in Switzerland. Sanitation, a greater than common attention to diets, and careful studies in animal behavior have combined to allow Zolli to break numerous records. First to reproduce pygmy hippos and the disappearing Indian one-horned rhinoceros, it has carried both species into successive generations when few other zoos could breed them at all. It has had similar success with flamingos, orangutans, siamang gibbons, spectacled bears and, most of all, gorillas. The large family group of these greatest of the apes is alike an attraction for ethologists, studying animal behavior, and zoo-goers in search of an hour's fascination.

Among Europe's many other zoos that would more than repay a visit, including a few that I know only by professional reputation, are those in Munich, Stuttgart, Hanover, and West Berlin. Not least is that father of all the free, open, cageless zoos in the world - the Stellingen Gardens near Hamburg. It is still notable for those ingenious optical illusions - the result of landscaping - that allow the viewer to imagine that animals only relatively free in fact are so free as to be almost on top of him.

In Switzerland don't neglect Zolli's excellent neighboring zoo in nearby Zurich. Belgium's small but highly regarded collection in Antwerp gets high ratings, as does the Zurich Zoo, for a strong scientific bent and an admirable role in the community's educational system.

Rome? Paris? Copenhagen? Let's just say that their zoos cannot quite compete with the myriad other attractions of those fabulous cities. I would even include the London Zoo in this category were it not for the superb scientific facilities that go along with good but not spectacular exhibits.

On our own side of the Atlantic the great number of zoos to pick from makes the task of selection even harder than in Europe. Directing a foreign zoo buff, with time but not distance a consideration, I should point him without fail to the New York Zoological Society's Bronx Zoo, to the Arizona-Sonora Desert Museum, 14 miles west of Tucson, and to the San Diego Zoo and its Wild Animal Park.

New York's Bronx Zoo, one of the world's greatest, has been enjoying a renaissance. For a decade scarcely a year has passed without some spectacular addition to this park, less than 40 minutes by express bus from midtown Manhattan.

Looking down, for example, from the open ''Bengali Express,'' a slow-moving monorail, a visitor to the Wild Asia exhibit sees what looks more like a stretch of the Irrawady than the Bronx River, its banks lined in turn by slices of India, Burma, and points east. Roaming free as far as the eye can see are, first, axis deer and barasingha, followed in the ''South China Hills'' by Formosan sika deer, all but extinct in the wild. Then comes the ''Tiger Machan,'' from which Siberian tigers can be seen bathing in a stream or swatting their pesky cubs. Asian elephants are on the loose at the next turn, and beyond them the prehistoric-looking Indian rhinoceros, which sometimes ambles to within a few feet of the leisurely paced train.

For the educational brilliance of its amusing graphics as well as the marvels exhibited, including the feeding of newly hatched birds, few shows in the zoo world surpass the World of Birds, already mentioned. And these are only two of a dozen first-rate innovations at the Bronx, not least of them a newly opened Children's Zoo where do-it-yourself activity allows young customers to play at being prairie dogs, fennec foxes, spiders, and turtles - all with appropriate equipment.

Probably the most distinctive zoo in the United States goes under the name of the Arizona-Sonora Desert Museum. It is a combination of museum, zoo, botanic garden, and nature trail - all in a desert setting against a backdrop of saguaro cactus 40 and 50 feet tall, desert blooms, and mountain ranges that seem to change color from hour to hour.

Among the features of this regional center are an underground tunnel for burrowing creatures, seen through glass panels in the tunnel walls; natural displays of such local fauna as black bear, bobcat, puma, prairie dog, and Mexican wolf, and a newly completed Earth Sciences Center, an expertly replicated cave that displays and interprets the geophysical history of the region, complete with stalactites, genuine minerals, and live bats. One of a kind, Arizona-Sonora is not to be missed.

To many a zoo-fancier, American or foreign, professional or amateur, the San Diego Zoo is the very model of what a zoo should be - visually, scientifically, and for plain good fun. Actually, two animal collections make up the complex, and the visitor owes it to himself to see both: the 128-acre zoo in the heart of San Diego and the 1,800-acre Wild Animal Park in the San Pasqual Valley some 30 miles to the north.

Both segments enjoy a climate that is the envy of almost every other zoo in the world - balmy the year round, with an annual average of 330 days of sunshine. This happy circumstance permits permanent open-air quarters for practically all the animals, with none of the worry and expense of seasonal shifts and changes. It also permits botanical displays that are unsurpassed anywhere. The flowers and trees range from orchids, palms and aloes all the way up to giant redwoods, besides such popular favorites as magnolia, flowering peach, and crabapple. The park's flora are in fact worth more than all its fauna combined.

From the very entrance - which momentarily appears to be a lush stage set rather than an exhibit of live pink flamingos against a tropical background - the eye is won over. Particularly charming, it seems to me, are the shy koalas, models for the teddy bear, enjoying the privacy of a tree refuge, yet not too hidden to be seen munching away on their home-grown eucalyptus. Likewise the lofty walk-through aviary, the big-eyed lemurs, and the view, in the nursery, of infant primates downing their bottled formulas.

The Wild Animal Park is a considerable contrast. While its purpose is to supply San Diego and many other zoos with specimens, the show it puts on is, for the most part, spectacular. As open as a zoo can get, it has pioneered in mixing animals, as far as possible as they are mixed in nature. From the two-car monorail that circles the project, one sees, as on the Serengeti plain, zebras, wildebeest, gazelles, impalas and ostriches - living and moving in natural groups. Thanks to hidden barriers, the viewer is unaware of any separateness when he then comes suddenly upon a troop of white rhinos or a pride of lions or giraffes galloping off in their stately manner, showing the way to gazelles and leaping impalas. On a space scale that other zoos can only dream of, it is without doubt one of the greatest shows in the zoo world.

If most of America's fine zoos are not dwelt on here, it is not for lack of excellence. Many are compressed into small areas in the midst of cities, where educationally they are most needed but where lack of space is a constant inhibition. Yet an astonishing number are firstrate.

The National Zoo in Washington is surely among the foremost of these, and so are Chicago's Lincoln Park Zoo, with its remarkable collection of primates, and the Philadelphia Zoo, which boasts a new and glamorous ''Bear Country.'' Brookfield Zoo, on Chicago's outskirts, is notable for its new and gigantic Tropic World, in which gorillas, birds and monkeys are to be viewed indoors, yet without the disadvantage of glass or bars, the animals separated by moats from the indoor jungle paths that accommodate their observers. Superior in other ways are the fine collections in, among other cities, Cincinnati, St. Louis, Milwaukee, Oklahoma City, Omaha, Seattle, and Los Angeles.

Among the newer and more innovative zoos are those of Minnesota's Apple Valley, just south of Minneapolis, where four multilevel trails take the walker into four worlds of animal life, each with the appropriate setting, fauna and even climate, and Topeka's rebuilt zoo, with its Tropical Rain Forest under a geodesic dome that allows natural light to fall on its varied Amazonian scenes. Miami's still uncompleted Metrozoo, given the climate, a totally cageless plan, and its informative ceramic pictographs, promises to be another national gem.

These - and no doubt a dozen others - should be visited not only by zoo-lovers but by zoo critics, especially those who still think of zoos as the wretched small-caged ''bastilles'' that they may have known and smelled in their childhood; who are not aware perhaps that the really good modern zoo is even now the last best hope for preserving such adornments to this planet as the tiger and the snow leopard, the condor and the okapi, the gorilla and the giant panda. Arizona-Sonora Desert Museum Hours: summer - 7 A.M. to sundown; winter - 8:30 A.M. to sundown. Location: Fourteen miles west of Tucson on Route 9. Admission: $5; $2.25 juniors; 75 cents children. Acreage: 12. Special features: Desert flora and fauna, area geohistory at Earth Sciences Center. Basel Hours: summer - 8 A.M. to 6:30 P.M.; winter - 8 to 5:30. Location: Binningerstrasse 40, Basel. Admission: $3; $1.25 children. Acreage: 29.6 Special features: Flamingos, pygmy hippopotamuses, large family of gorillas. Bronx Hours: 10 A.M. to 5 P.M.; 10 to 5:30 Monday and holidays. Location: Fordham Road and the Bronx River Parkway. Admission: $2.50; 75 cents children; no charge Tuesday, Wednesday or Thursday. Acreage: 264. Special features: World of Birds, Wild Asia, Children's Zoo. The world's largest urban zoo. Durrell Hours: 10 A.M. to 6 P.M. Location: Northeast corner of Jersey in the Channel Islands. Admission: $3; $1.40 children. Acreage: 23. Special features: More formally the Wildlife Preservation Trust, it is a haven for small endangered species. Frankfurt Hours: summer - 8 A.M. to 7 P.M.; October - 8 to 6; winter - 8 to 5. Location: Am Tiergarten. Admission: $2.50; $1 children. Acreage: 27 Special features: The Exotarium, with rare birds and fish and Antarctic replica. National Hours: summer - grounds 8 A.M. to 8 P.M., buildings - 10 to 6; winter -grounds 8 to 6, buildings 10 to 4:30. Location: 3000 Connecticut Avenue, N.W. Acreage: 167. Special features: Chinese pandas and white tigers. San Diego Hours: summer - 8:30 A.M. to 6 P.M.; winter - 9 to 5. Location: Zoo Place, Balboa Park. Admission: $4.75; $1 children. Acreage: 100. Special features: Opening Sept. 25, the Whittier South East Asia Exhibit, with orangutans, gibbons, langurs, pygmy chimpanzees and exotic birds. Wild Animal Park - Hours: summer - 9 A.M. to 9 P.M.; winter - 9 to 4. Location: Highway 78, 30 miles north of San Diego. Admission: $5.25; $3.50 children. Acreage: 1,800. Special features: 5-mile narrated monorail tour, three free animal shows daily. Toronto Hours: summer - 9:30 A.M. to 7 P.M.; winter - 10 to 4:30. Location: Highway 401 East, Meadowvale Road. Admission: $3.20; $1.20 youths; 80 cents children. Acreage: 710. Special features: Asian, African animals and glass-enclosed area for polar bears. Whipsnade Hours: 10 A.M. to 6 P.M.; Sunday and banking holidays - 10 to 7. Location: Dunstable, 30 miles from London. Admission: $4.30; $2.20 children. Acreage: 500. Special features: Cheetahs, white rhinoceroses, polar bears.