A look at century-old Bering Sea art; Inua: Spirit World of the Bering Sea Eskimo, by William W. Fitzhugh and Susan A. Kaplan, with contributions by Henry B. Collins, Thomas Ager, Dorothy Jean Ray, Saradell Ard Frederick. Washington, D.C.: Smithsonian Institution Press for the National Museum of Natural History. 295 pp. $12.50 (paperback).

Eskimo life of a century ago was no picnic. It may have had a coherence now lacking, but it certainly was difficult. Edward William Nelson discovered how difficult when the Smithsonian Institution sent him to the Bering Sea area of ''Seward's Folly,'' acquired only 10 years previously from Russia.

Nelson was in Alaska from 1877 to 1881, gathering all the information he could about this virtually unknown territory. He was extremely thorough in his researches and in making a magnificent collection of material pertaining to all aspects of Eskimo life.

Now the Smithsonian is circulating a portion of the collection in Alaska, and has produced the book to go with it. Essays by scholars who have studied the collection give a clear picture of the strenuous life of these Arctic people, while at the same time drawing upon Nelson's reports and notes to give an idea of the rich inner life that enabled the people to cope with their harsh, but often beautiful, environment. Unfortunately, Nelson's diaries have not yet come to light, so we can only guess at his own reactions and feelings.

The Eskimos were amused at Nelson's interest in their everyday artifacts and called him ''the man who buys good-for-nothing things.'' What will they think now of his efforts to preserve them - and to tell the people of the lower 48 states what they had a century ago?

Their dance masks, for instance, now are regarded as the peak of the craft, clearly revealing the inner characteristics and artistry of their makers. Everything, even bowls or clothing, was thought to possess a spirit. It appeared as a semihuman face in such things as representations of caribou or bear in masks, or on boxes in the form of another important animal, the seal. Animals and objects always had to be treated with the utmost respect in order to keep the respect of the inua, or spirit.

The Bering Sea Eskimos developed a fairly elaborate culture in their unique and relatively well-supplied coastal situation, bypassed for nine centuries of European exploration. This book may help us appreciate what they have to offer, even as it provides an exercise in ''reading'' art. Certainly it shows how art and life are bound together for a people directly dependent upon the natural world and acutely aware of that dependence.