Frank Church came to Washington from Idaho in 1957 as the youngest member of the Senate, age 32 and mistaken for a page, a fellow who "slid down bannisters in public places" to the intense embarrassment of his 10-year-old son Frank Forrester Church IV, called Forrest. Church, a liberal Democrat, served in the Senate for 24 years, the last two in the post he had set as his goal at 14, the chairmanship of the Foreign Relations Committee. It had long been the domain of his hero, rebel Idaho Republican William E. Borah.

Church was defeated in the Reagan landslide of 1980 and died of cancer in 1984 at 59. To his admirers he was a tower of truth and integrity who early came to see the Vietnam war as a colossal blunder and who valorously exposed the machinations of the multinational corporations and the intrigues of the Central Intelligence Agency. To his detractors he was a naive do-gooder, at heart an isolationist like his hero Borah and an unwitting, at best, appeaser of communists.

In truth, there indeed was something about Church akin to Jimmy Stewart's portrait of a senator in "Mr. Smith Goes to Washington."

This small volume, however, is not at all another biography of a senator. Rather, it is a son's tortured account of his relationship with his father, who happened to be a senator while his son was becoming one of the victims of the very war his father opposed. He became estranged from his father because he, the son, felt that "as far as I could see it, everything my parents were involved in, belabored as it was with inevitable compromise, was a sham."

So what's new? Our literature has been flooded with such stories. And this particular son is not the only one now to state candidly that he enrolled in a divinity program "to avoid the draft."

What makes this account worth reading is that the son, today the 36-year-old minister of All Souls Unitarian Church in Manhattan's Upper East Side, has struggled so hard, in print as well as in private, to come to terms with his own life, his parents and his sense of religion. He is not a felicitous writer but there is a rugged honesty about his words at times reminiscent of what he calls his father's "most characteristic trait, a sense of outrage against practices . . . he believed to be morally wrong."

The irony, of course, was that as the father was defying the man who had helped him up the Senate ladder, Lyndon B. Johnson, and was "writing the legislation that would finally put a stop to the invasion of Cambodia," the son thought the American system was finished.

The father's -- and the mother's -- pain is evident. The son's marriage at 21 to a 19-year-old fellow student with whom he was living "in a commune of sorts, complete with a dog, two cats, and a goat," and the evolution of that marriage are intriguing, but one would like to have more than a one-dimensional picture of wife Amy, who would become the youngest dean of students at Harvard Divinity School and the mother of "Twig" and "Spud."

This family story is, in many ways, not an unfamiliar one in Washington, save perhaps for the enduring love affair of the senator and his politically astute wife Bethine, the daughter of a governor. The son discloses that his mother opposed Church's 1965 speech against growing American involvement in Vietnam. And I had not read before that L.B.J.'s famous rejoinder, "The next time you want a dam in Idaho, you go to Walter Lippmann," was not what the president had said but what L.B.J. "wished he had said to me . . . So the next day he told the press he had said it anyway." But it is left to a true biographer to write the book on the senator.

Forrest Church has tried to put down a portrait of "myself and that part of my father that is in me." The result is much soul-searching and much about religion in this story of estrangement and reconciliation.

Frank Church was raised a Catholic, listed himself as a Presbyterian and gave his son, then 10, Thomas Jefferson's "The Life and Morals of Jesus of Nazareth," a little book of excerpts from the Gospels emphasizing "Jesus' ethical teachings by striking out such things as the virgin birth and the resurrection." Jefferson was to become their "common ground," especially this passage father quoted to son: "It is in our deeds and not in our words that our religion must be read."

Thus the son "cannot embrace a dogmatic faith." Thus he believes that "Life is a miracle couched between mysteries" and that this "miracle . . . is not wholly accidental." And the son's own "unorthodox view of God" is that "God is our name for the spirit that animates and impels and finally infolds our lives into his own." Just as the father died "at peace with himself," so the son seems finally to have reached a peace within himself.