The indigenous and once-celebrated American buffalo (Bison bison), as absent from the National Zoo in recent years as from the nickel, returned to its former home on Connecticut Avenue yesterday freighted anew with history and environmental instruction.

The new arrivals, two 1,200-pound females purchased from the Burnet Park Zoo in Syracuse, N.Y., are the first buffalo displayed here since their predecessors were shuffled off to other zoos in 1965.

Prior to that buffalo were something of a zoo mainstay, and, in fact, grazed the Mall in the 1880s, before the zoo was ever built, as live models for taxidermists at the Smithsonian Institution.

In those days the buffalo was a rallying symbol for conservationists mindful of the dwindling resources of a vanishing frontier.

Once adrift on the Great Plains in vast herds, the shaggy animals had been hunted to the edge of extinction by hide-hunters, meat packers and tongue picklers as well as trigger-happy travelers who casually slaughtered them by the thousands from the windows of passing trains.

By the turn of the century, the number of buffalo in the United States had dwindled from an estimated 60 million to fewer than a thousand, protected in a handful of parks and private herds. Naturalists were uncertain of the fate even of those.

By the 1960s, however, the durable species had proved all it needed was to be left alone. The herds had so multiplied that buffalo fanciers from Virginia to California were raising them for meat as well as memory, and breeding them into cattalo and beefalo with domestic cattle.

Today, when Washingtonians in quest of the frontier experience can sample buffalo steaks at Dominique's Restaurant or the International Safeway, more than 70,000 buffalo are prospering in parks and game preserves around the country.

Zoo spokesman Mike Morgan said the National Zoo never really wanted to get rid of its buffalo, but the animal's very ecological prosperity brought it into conflict with prevailing zoo philosophy.

"During the 1960s it was felt the zoo should concentrate on rare and endangered animals which the public had little opportunity to observe in other places," he said. "We had bison herds right out in Fairfax County."

In addition, he said, space was at a premium in 1965 as the zoo redesigned its hooved animal houses, and the animals were never replaced.

The two new arrivals, who have not been named, will be housed in an enclosure near the small animal house last used by a six-year-old rare black rhinoceros named Nipo. Nipo, he said, has been sent off to visit a female black rhino in Seoul, Korea, with instructions to be fruitful and multiply.