Rich, fluent Australian novel; Just Relations, by Rodney Hall. New York: The Viking Press. 502 pp. $17.75

This large Australian novel charts the course of a battle between advocates of ''progress'' and modernization and an ingrown, tradition-bound populace bent on keeping the 20th century at bay.

The setting is Whitey's Fall, a former gold mining town, whose 49 inhabitants - dairy farmers and their families - are mostly aged 90 or older. Their truculent resistance to ''improvements'' offered by Australia's Aesthetic and Historical Resources Commission powers a complex and amusing plot whose unraveling reveals the interrelationships of a vast, vivid host of sharply drawn characters.

The elders' stubborn clinging to their simple way of life is appealing, but Hall refuses to sentimentalize this willed primitivism. As we learn the long-withheld secrets of Whitey's Fall and see how its insularity has shaped its citizens, we measure their yearning for the old ways against warnings to ''get out of there if you've got any sense'' - and realize that the novel stays carefully, teasingly balanced between these extremes.

''Just Relations'' owes much to Joyce's ''Ulysses'' and Garcia Marquez's ''One Hundred Years of Solitude,'' but is, nonetheless, an original work distinguished by fluent style, colorful inventiveness, and plain old-fashioned narrative momentum. It's one of the richest novels of recent years.