FICTION : SUPPLY OF HEROES by James Carroll (Dutton: $17.95; 403 pp.).

James Carroll has woven a fine historical novel from the tangled threads of the conflicting loyalties--personal, religious, national--that have been the bane of “pinched, troubled” Ireland for centuries.

The plot is as timely as today’s grim reports from Northern Ireland. Yet, it centers on events that occurred nearly three-quarters of a century ago--the middle years of World War I when all Ireland was still under British rule. The war offers, or seems to offer, an opportunity to Irish nationalists for ridding their country of its British masters, even if it means making a pact with the devil, in this case Imperial Germany.

The novel focuses on Douglas Tyrrell, the son of a prominent Protestant Anglo-Irish family that is caught in the passions of the war and the desperate, harebrained effort “lost in the green fog of Irish dreams” to free Ireland that ends in the disastrous Easter Rising of 1916.

Douglas’ sister, Jane, personifies the novel’s conflicts. “In Ireland, she feels English. In England, she feels Irish,” and nowhere does she feel at home, that is, until she meets a Dublin actor-turned-revolutionary who speaks for the poor Catholics of Ireland. His love provides the roots she was seeking.

The book reveals a mixture of exasperation and affection that Carroll feels for the land of his ancestors. It is, finally, a plea for tolerance and brotherly love between Irish Catholics and Protestants that goes well beyond the novel’s time element. Carroll, a former Paulist priest, appears to be directing his sermon to the present conflict in Ulster.