Land of fire and ice - and the glories of ancient Maori art; Native New Zealanders strive to preserve their rich cultural heritage

New Zealanders like to speak of their country as ''a land of fire and ice.'' Ice abounds in the towering, glacial mountains of the South Island. The fire, on the other hand, is buried in the North Island.

It heats thermal springs that boil from deep within the earth, rumble ominously, spurt to spectacular heights, deposit mineral terraces of great luminescent beauty, and flow out into lakes of brilliant green and aquamarine.

The center of this thermal activity is Rotorua, a lovely but evil-smelling city in the heart of the North Island. Since the 19th century, when someone concluded that the sulfurous springs held soothing properties, Rotorua has been the place to ''take the waters.''

But long before the ''Pakehas'' (Europeans) became enthralled with the thermal springs, the Maori people were literally living on top of them. At Whakarewarewa, a thermal area within Rotorua, the small frame houses of the Maori stand amid smoking mineral caldrons. Women lower their cooking pots into communal ''ovens'' above steaming hot pools, and they heat their teakettles in boiling streams as an angler might cool a soda in a trout stream.

To this awesome place, visitors come these days not to take the waters (the central bathhouse, an enormous building of considerable Victorian charm, has become a museum) but to partake of Maori culture.

An eastern Polynesian people, the Maori originally migrated to the land they call Aotearoa, the ''land of the long white cloud,'' about 1,000 years ago. Maori traditions speak of a prosperous homeland, the island of Hawaiki, which modern scholars locate in the Society Islands (Tahiti), the Cooks, or the Marquesas. And most Maori trace their ancestry and take their tribal name from one of the outrigger canoes which, according to legend, came to Aotearoa during the 14th century in a ''Great Fleet.''

(That notion of deliberate migration by skilled Polynesian navigators was long disputed by scholars, who hypothesized instead a chance migration of lost and drifting canoes; but recent computerized research, which demonstrates that it is virtually impossible to run aground upon New Zealand by accident, seems to vindicate the Polynesian navigators and the Maori legend.)

The Maori brought with them the staple root vegetables, kumara and taro, and the gardening skills of their Polynesian homeland; and they imported the Polynesian dog whose fur proved useful in the colder climate of Aotearoa. They found a land that lacked mammals but was rich in aquatic life and birds, including many flightless species such as the 10-foot-tall moa, which the Maori apparently hunted to extinction, and the kiwi, which survived to become the national symbol of New Zealand.

When Capt. James Cook visited New Zealand in 1769 to map it for the Crown, he found diversity and much prosperity among the Maori communities. James Banks, the artist who accompanied Captain Cook on his visit, was particularly impressed by the quality of the woodcarving he observed at Tolaga Bay.

The men, he said, ''have a particular taste for carving: their boats, paddles , boards to put on their houses, tops of walking sticks . . . are carved in a variety of flourishes, turnings, and windings that are unbroken; but their favorite figure seems to be a volute, or spiral, which they vary many ways, single, double, and triple, and with as much truth as if done from mathematical draughts: yet the only instruments we have seen are a chisel, and an axe made from stone.'' That remarkable carving proliferated further when Cook and other Europeans introduced steel tools, enabling the Maori to build bigger meetinghouses and war canoes and to decorate them more elaborately.

But the Europeans also brought muskets (which turned Maori skirmishes into massacres), epidemics, and an unscrupulous lust for land. When in 1840 some Maori chiefs signed the Treaty of Waitangi, giving the English Crown the sole right to purchase Maori lands, the Maori outnumbered the ''Pakeha'' 10 to 1. A generation later, decimated and overrun by Pakeha settlers, and struggling merely to survive, many tribal groups gave up their traditional arts altogether. In 1910, while anthropologists predicted their extinction, the Maori established their first art school - Te Aomarama - at Rotorua to preserve artistic traditions and to revive tribal styles that had died out. The concept of Te Aomarama was revived 20 years ago in the institute which flourishes at Rotorua today. But the great classical art of the Maori is not at Rotorua. Much of it remains in the care of Maori communities, where it is kept from public view.

But now, for the first time, a major exhibition of Maori art has been assembled by the American Federation of Arts, in cooperation with the New Zealand government, the Maori people, and 13 New Zealand museums. The show, ''Te Maori: Maori Art from New Zealand Collections,'' will be at the Metropolitan Museum of Art in New York from Sept. 10 to Jan. 6, 1985, the Saint Louis Art Museum from Feb. 22 to May 26, 1985, and the M. H. de Young Museum in San Francisco from July 6 to Dec. 1, 1985. (The show, many years in the planning, is made possible by the support of Mobil, Air New Zealand, and the American National Endowments.)

The exhibit includes almost 200 Maori sculptures and carvings in wood, stone, bone, ivory, and shell, produced between 1000 and 1880, representing some 30 tribal styles, and ranging in size from the 13-foot gateway of the Pukeroa fortress to tiny personal ornaments of ivory and jade. Never before has such a collection of Maori work been gathered together, and never have these ancestral treasures - the true fire of Aotearoa - been allowed to leave their homeland. Even now they will be accompanied by Maori elders, who will perform ceremonies at each of the museums to lift the tapu (taboo) and safeguard the ancestors commemorated in the carvings.

The mana (prestige) of the Te Maori exhibit has already shown its effects in New Zealand. Many Pakeha New Zealanders are looking again at the art they have taken for granted as merely ''primitive.'' And the Maori, who played a major role in planning the exhibit, are gaining new self-esteem from their ancestral art. A Maori proverb holds, ''He toi wkakairo, He mana tangata.'' ''Where there is artistic excellence there is human dignity.'' The excellence and the power of Te Maori should not be missed.