Celtic history, language, culture; The Celtic Consciousness, edited by Robert O'Driscoll. New York: George Braziller.642 pp. $40.

This unusual book comprises 48 essays given during a symposium at the University of Toronto, in which many of the world's leading Celtic scholars shared some of their recent remarkable findings about the Irish, Welsh, Scottish , Cornish, and Breton peoples who historically shared the Celtic language. To their credit, the scholars speak in the kind of accessible way that we have come to expect of real leadership in any field.

The editor, Dr. Robert O'Driscoll, has a man-for-all-seasons quality. He's at home in Celtic archaeology, the fastest-growing field of archaeological study in Europe, and equally at home in Celtic history, linguistics, literature, music, art, and social and cultural anthropology. The evidence he marshals here seems to substantiate Claude Levi-Strauss's remark that the roots of Western civilization lay less in the Mediterranean than in the great pre-Roman Celtic presence. (The Celts dominated central and northern Europe during half of the first millennium BC; the Romans referred to them as ''Gauls.'')

The revival of interest in Celtic literature at the end of the 19th and beginning of the 20th centuries was marked more by an intuitive understanding and appreciation of the ancient legends and verses than by thorough research and rock-ribbed fact. Yeats and other key figures in the ''Celtic revival'' believed there had to be and eventually would be the kind of substantial, verifying, scholarly work which this book so ably demonstrates.

In these varied pages one becomes deeply aware of the Celtic mode of perception - that numinous way of seeing supernatural influences in ordinary events, and the accompanying reflective process that feeds the sense of the supernatural and develops a simultaneous interplay of person and world and spirit.

There is very little of a political nature in this book, its ground being grander and more abiding. It succeeds in revealing the elements and possibilities inherent in the Celtic spirit - an attractive text, useful to any thoughtful person, but especially valuable for Irish readers who want to integrate responsible history and facts into their meditations on their cultural heritage and identity.