Gift ideas -- choicest new books for the holidays; Hopis reveal secrets; Hopi, by Susanne and Jake Page. New York: Harry N. Abrams. 240 pp. $50.

American Indians say that the oldest tribe of them all is the Hopi. Many also regard the Hopi as the wisest and the most resourceful. Their name means the peaceful people. Their religion is a constant response to the desert, the sky, the rain, animals. They invest Arizona with their sacred places and their culture, and fight for its preservation.

Tradition and modernity struggle in their clans, are reconciled, and then struggle again. Since the Hopi are a very private people, they do not share themselves or their ways, for they do not trust the whites. But they trusted Susanne and Jake Page (after many tests) to live with them and tell ''what many Hopi people - though by no means all - wanted us to know about them, their lives and their concerns.''

The result is a sensitive and valuable documentation of a remarkable people - a beautiful book, rich in language and very rich in photographs.