The publication on Independence Day 1981 of the concluding volume of Dumas Malone's great Jefferson biography has inspired almost as much celebration of the author as reflection on the post-presidential years of his great subject.

That is fitting. We prize gallantry where we find it. And there is gallantry in Malone's splendid conquest of what Mr. Jefferson himself called the tedium senectutem: the weariness of age. The Sage of Monticello (Little, Brown, $19.95), undiminished in scholarship and felicity of style, is the serene and sympathetic, if not uncritical, chronicle of one distinguished octogenarian by another who long ago earned the right to call him a friend. The sage of Monticello was a marvel. So is his biographer.

When Thomas Jefferson left Washington forever at the end of his troubled second term in 1809, he was judged by not a few to be a failed chief executive and a political theorist of dubious influence. By all this, if not by the tormenting personal debts he shared with the Virginia gentry of his time, Thomas Jefferson was largely untroubled. His was a sunny spirit, not easily downcast. Not much earlier he had written that "our cloudless sky ...has eradicated from our constitutions all disposition to hang ourselves, which we might otherwise have inherited from our English ancestors."