THE BOOK OF HOURS, With a Historical Survey and Commentary, by John Harthan (Crowell, $29.95). In recent years, a significant number of art books have been dedicated to complete productions of the more notable medieval books of hours - those personal prayer books with superb illustrations which were commissioned by members of the pre-Gutenberg nobility.In contrast, this survey offers a synoptic view of that unique art form. It presents samples from 34 manuscripts, dazzling in the variety of styles from primitive Gothic to the first stirrings of the Renaissance, tantalizing in their indication of further riches to be explored. The reproduction and commentary are excellent.

ITALIAN RENAISSANCE ILLUMINATIONS, by J.J.G. Alexander (Braziller, $19.95; paperback, $9.95). Less intensively explored in current art books than medieval illuminations, these manuscript illustrations of a slightly later period have a considerably larger range of subject matter (including the works of such writers as Dante, Petrarch and Virgil, natural history, astrology) and a more consistent level of expertise in such technical areas as vanishing-point perspective. What is gained in polish is lost, of course, in fresh naivete of vision, but this book offers a fascinating glimpse of a relatively unknown branch of art.

CELTIC AND ANGLO-SAXON PAINTING: Book Illumination in the British Isle 600-800, by Carl Nordenfalk (Braziller, $19.95; paperback, $9.95). This will interest those who are impressed with the intricate illuminations in the Book of Kells. Through 48 color plates, each with its own commentary, and a general introduction, Nordenfalk traces the development of Celtic illumination which culminates in the Book of Kells , as well as the Anglo-Saxon influence - their Germanic sense of order and their new motifs - on Celtic illumination which culminates in the Book of Kells. Royal patronage gradually shifts the centers of artistic influence from Ireland to Scotland and Northumbria and later to Kent. Yet between the poles of Lindisfarne and Iona he sees "an electric arc of unusual luminous intensity" in Hiberno-Saxon art.