The golden glories of San Marco; Study of mosaics illuminates the tangled history of art, religion, and politics in Venice; The Mosaics of San Marco, by Otto Demus. Chicago and London: University of Chicago Press, 1984. Vol. 1: 489 pp.; Vol. II: 242 pp.; Vol. III: 357 pp.; Vol. IV: 280 pp. Entire set: $300 until 1/1/85, $350 thereafter.

''Gold pervades everything; it glides over rounded edges and corners, invades niches and recesses, and penetrates all figural compositions.'' Art historian Otto Demus thus describes the stunning rich goldenness of the interior of the Basilica of San Marco in Venice, where a shimmering mosaic skin, punctuated with colored images sacred to Venetians of an earlier day, seems to cover every surface above the arcade level.

In his four-volume work, ''The Mosaics of San Marco,'' Mr. Demus deals exclusively with those mosaics made before 1300. His detailed and comprehensive study is the first in nearly a century - and the first in the English language - to examine the stylistic and iconographical program of the early basilica as it evolved from a mostly borrowed Byzantine to a distinctively Venetian style.

The establishment of a correct chronology was central to Demus's task; much of his research was conducted on high scaffolding to determine just how much of the mosaic surface is original and how much is restored or simply replaced altogether.

Demus adds the knowledge of a half-century of distinguished scholarship to this archaeological foundation and provides extensive illustrative material - no less than 160 high-quality plates in color and 857 in black and white, including text illustrations. In doing so, Demus has laid the groundwork for future generations to pursue in depth a wide range of questions that have surrounded the origins of Venetian art and its uniqueness within the larger Italian context.

A major strength of the book lies in Demus's lucid and intricate unraveling of the various stylistic strands - early Christian, Byzantine, French Gothic - that were woven into the indigenous Venetian mural tradition over a period of about 200 years. The reader is enabled to follow the emergence of a new artistic style that was not simply a mixture, but a genuine synthesis that resulted in something essentially new.

Demus finds, moreover, that in the process a multiplicity of individual styles developed within the common framework, thus allowing artistic creativity and innovation to flourish even within conditions of close cooperation.

Nor should we think that a more precise dating of the various mosaics is of interest only to art specialists. Such information is essential for understanding the dynamic role of art in the political as well as in the religious life of the period. Venetians, indeed, would have found the distinction between politics and religion puzzling. For in these mosaics, the religious theme of the history of salvation is intertwined with the political theme of the life of St. Mark and the translation of his relics to Venice. Demus analyzes this program's development in the mosaics from the 11th through the 13 th centuries. His work offers precious visual evidence of the birth of the Venetian state church and of a uniquely successful civic ideology that became the envy of many a European polity.

Demus's book will be of interest not only to specialists in the medieval period, but also to students, scholars, and interested observers of later Venetian art as well. Allowing that the Venetian mosaics had little impact on art elsewhere in Italy, Demus stresses that they had a long and influential afterlife within Venice itself. For the Venetian taste for a subtle and rich colorism that characterizes so many paintings of the Renaissance period was formed and nurtured by the constant visual presence of the mosaics of the basilica.

From the literal reproduction of golden mosaic apses in the paintings of Giovanni Bellini and Lorenzo Lotto, artists like Titian and Tintoretto would move toward a virtual translation of their optical effects with intangible, immaterial backgrounds that remain as ungraspable as their models - the mosaics that seem to change constantly with the changing light.

Furthermore, the wide compositional formats of Carpaccio and the other narrative painters of the scuole, who unrolled the story line in a leisurely manner across the ground plane rather than focusing it with the dramatic concentration of Tuscan artists, found their direct ancestors in the mosaics of the 13th century.

Finally, the rejection of framing devices by the medieval mosaic artists would allow Tiepolo and Piazzetta to conceive of their great vault decorations of the 18th century in terms of a unitary and unbroken surface.

This book, a masterpiece of loving and exacting scholarship, is a reminder to the present-day visitor to San Marco that he or she is not simply looking at an isolated fragment of an alien Byzantine past, albeit a ''wonder of the world.''

Standing with Demus where Bellini, Carpaccio, and Titian once stood, we can witness the genesis of a long artistic tradition wherein those qualities that would come to define the art and culture of Venice for centuries to come were first set out within the genre of mosaic.