THE IGBO peoples of southern Nigeria see everything as relative, including their relatives, whether living or dead. The real and spirit worlds intertwine, so that the extended family embraces not only grandparents and cousins but countless ancestors who take a benevolent, spiteful or even deadly interest in the lives of the living.

To honor or propitiate the spirits of the dead requires ceremony and sacrifice, but mainly it requires statues, shrines and masks, a rich selection of which forms the core of "Igbo Arts," a new exhibition at the Smithsonian's National Museum of African Art.

Although their culture is ancient -- they were casting wonderful, intricate bronzes a thousand years ago -- the works are always fresh, as though each artist felt he were creating the traditions himself. The driving force is Ike, the individual energy that flows in everything in the Igbo world, material or spiritual, living or dead, good or evil.

"In some cultures an individual may worship one of the gods or goddesses in the pantheon and pay scant attention to the rest," says Igbo novelist Chinua Achebe in his foreword to the exhibit's fine catalogue. "In Igbo religion such selectiveness is unthinkable. All the people must placate all the gods all the time!"

None of the pieces in the exhibition dates back much more than a century. Older ones are rare because although the Igbo artist's work is often heroically painstaking, no special effort is made to preserve it. Splendid mbari houses, shrines filled with art objects, are purposely neglected, and the tropical climate and termites make short work of them. Since the Igbo value the process rather than the product, Achebe says, it is well that the works should wither away, so that succeeding generations can make their own.

The Igbo are most famous for their masks, ranging from simple cutout calabashes to vast assemblies as much as 20 feet high, all used in dancing masquerades. Spectators are expected to dance also, to achieve the proper spirit; dance so embodies the Igbo concept of the fluidity and impermanence of all things that the dead are danced to their graves.

Assembled by the Museum of Cultural History of the University of California at Los Angeles, the exhibit is fascinating, although necessarily a mixed bag. In an attempt to give context to the objects, they are grouped according to whether they primarily relate to the individual, the extended family or the community. But such classifications are foreign to the Igbo way. As Achebe says, "The very concept of collections (is) antithetical to the Igbo artistic intention."

IGBO ARTS: COMMUNITY AND COSMOS -- Through October 13 at the Smithsonian's National Museum of African Art, 318 A Street NE. Special programs associated with the exhibition will include lectures, docent tours and workshops; for children there will be maskmaking, storytelling and body painting. Call 287-3490 for details.