When Europe discovered Greece; Early Greek Travellers and the Hellenic Ideal, by David Constantine. Cambridge, England: Cambridge University Press. 241 pp. $49.95.

In the ''Travel Report'' that accompanies Christa Wolf's ''Cassandra: A Novel and Four Essays,'' she asks, ''Who would want to be the monster left indifferent by the Acropolis of Athens?''

The question is not simply rhetorical. No one wants to be considered a monster, regardless of the description. Wolf knows that monsters were rife during the Turkish occupation of Greece; neither the conquerors nor the conquered seemed to care about the Acropolis. It is only with the sentimental antiquarians discussed in this book that the Acropolis achieved its place in the imagination.

Wolf herself visited the Acropolis (''... floating in the deep-blue sky like an airship ...'') as part of her own Aneignung, that is, appropriation, of the spirit of Cassandra, the prophetess whose rejection of Apollo was punished by the god so that she was never taken seriously again. Cassandra preoccupies Wolf.

The astonishing vigor of Christa Wolf's Cassandra reflects a larger phenomenon, the Greek phenomenon. In ''Early Greek Travellers and the Hellenic Ideal,'' David Constantine discusses travel as one of the forms enthusiasm for ancient Greece assumed in the 17th and 18th centuries: travel - to Rome, where Roman copies of Greek sculpture were often taken for originals, and less frequently to Greece. The travelers - Lady Montagu appears to have been the only woman - included ''botanists and clerics, Oxford scholars, aristocratic dilettanti, ambassadors, merchants and adventurers. They knew their Bible, their Homer, Herodotus, Strabo and Pausanias, or Montesquieu, Rousseau, Spence, Winckelmann and Webb.''

The ''or'' here is significant. The pull of Greece first asserted itself in the schoolrooms where 17th- and 18th-century students read Homer, but their contemporaries such as Rousseau reinforced their desire to see Homer's land by awakening a desire to come into contact with peoples untouched by Christian civilization. And Montesquieu taught that a people's character survived ''despite the interferences of history.''

Yet the interferences cast spells of their own. A desire to travel is, in part, a function of the desire to escape oneself or at least one's homeland. For these antiquarians - some of them , but not all, scholars - Greece added the further enticement of being not really itself. What they came to see were ruins. So the flight of the early Greek travelers was both spatial and temporal. These travelers left England, France, and Germany to discover the Hellenic Ideal.

Nostalgia involves homecoming. The closest to Greece Johann Joachim Winckelmann came was Paestum, in southern Italy. But, as papal antiquary starting in 1763, it was his responsibility to keep track of the new ''finds'' turned up by more vigorous travelers. He did a little collecting on the side; the head of a faun was his dearest possession.

Constantine writes powerfully of Winckelmann's sensuality; pictures and statuary that embodied the Hellenic Ideal can have a powerful erotic appeal. Winckelmann's failure ever to visit Greece and his violent death on the road north seem to be two sides of one coin. The great connoisseur, in daily contact with beautiful things, at last chose to go home.

What possessed these travelers was, among other things, the conviction that Homer read in situ was Homer clarified. Landscapes and peoples, customs and tools are the stuff of art; Homer's poetry, charged with heroism and tragedy, was rooted in time and space. So argued Robert Wood, the great Englishman whose essay on the originality of Homer (1767) did much to spread the itch for travel to Greece. Greek art copies nature, not formal patterns, as in French classicism. Constantine's book is, in essence, a meditation on the problems symbolized by the pairs art/nature and letter/spirit. And his discussion of Wood is fascinating.

In brief, this book is itself an eloquent defense of the ideal to which the travelers bore witness: ''Accurate knowledge is not detrimental to true love.... A single column is like a basic unit of aesthetic pleasure; it pleases the eye and the imagination in a peculiarly whole and substantial way....'' And in his ''Conclusion,'' Constantine asks, ''Why should not the imagination love precision?''

The last traveler discussed here is Richard Chandler. His prose is exemplary. Constantine quotes from his ''Travels in Asia Minor'' (1775) he wrote: ''We saw no traces either of houses, churches, or mosques. All was silence and solitude. Several strings of camels passed eastward over the hill; but a fox, which we first discovered by his ears peeping over a brow, was the only inhabitant of Laodicea.''

If only there were a modern reader's edition of ''Travels in Asia Minor!''