"THE INNOCENCE THAT I cherish in the arts," Stanley Kunitz once wrote, "derives from a capacity for perpetual self-renewal." Add Robert Penn Warren's remarks -- "I want variety . . . Man is interesting in his differences" -- and we are well on our way toward discovering the satisfying freshness of the latest books by two of our finest poets.

But the poetic energy does not come only from metamorphoses. Each poet is also committed to exploring limits and continuities, the forces of personal and public history within which transformations occur. For Kunitz the "vainest ambition is to want an art separated from its heritage, as though the tradition were a cistern full of toads instead of a life-giving fountain. A poet without a sense of history is a deprived child." Warren, more obviously obsessed by history throughout his long career, puts it simply that "only by knowledge does man achieve his identity." And it is knowledge that these two important books offer: in the recognitions of necessity, of complicity, of hope, and of what Kunitz describes as the "waking each day to the wonder of possibility."

In remaking Brother to Dragons Warren has slowly and securely sharpened both poetic and historical sense. Narrative line is more taut. Rhetorical gesture is minimized. Monologues are broken up, reassigned for firmer dramatic logic, and redistributed as parts of dialogue. And important historical figures like Meriwether Lewis are given fuller voice. The plot still turns on the psychological disintegration of Thomas Jefferson's nephew, Lilburne Lewis, who with his brother Isham murdered and mutilated a slave in the meathouse of their Kentucky wilderness plantation. But even more pointedly than 26 years ago when the first edition appeared, Warren directs our attention away from the event toward the ways its reverberations may affect our thinking about a definition of the American experience.

Jefferson, not his nephew, is the protagonist here. He is the architect who offered up to an eager people the plan which was to shape our national character. We uould "redeem the wild land, set blossom by the stone." Beginning in an "upper room" in Philadelphia with the Declaration of Independence, the idea encompassed Louisiana and the West which, as Warren tells it, Jefferson "brought and gave and never/Saw, but like the Israelite,/From some high pass or crazy crag of mind, saw." And the plan extended to the president's brother-in-law, Charles Lewis, who, recognizing an "illusion," still sought with Jefferson a "new world, new birth, tension and test," to "renew, if for an instant only / . . . some part of human effort and man's hope."

Warren suggests convincingly that the idea was flawed from the first. The darkness in the land was also in the poor fumbling human beings who simply carried it with them to the wilderness: the savagery of the murder of the slave is evidence. And even more devastating is the suicide of Meriweather Lewis, Jefferson's "cousin . . . near-son," his "own blood" who had been sent to "name and chart and set the human foot." Instead of fulfillment, Meriweather discovered, as he proclaims with the bitterness of a disillusioned true believer, Jefferson's "lie," uncovering "in the end, the tracklessness / Of the human heart."

Even Meriwether mellows, though. For Warren is not out to dream a nightmare as our new historical vision. If we read sympathetically, as I believe Warren's fine individual characterizations and moving meditations compel us to, we discover, dreamers all, that Jefferson's idea was worth the anguish. As Lucy Lewis declares, "If there was vanity, fear, or deceit in its condition,/What of that? For we are human, and must work / In the shade of the human condition."

Stanley Kunitz is equally forthright in facing and communicating the hopes and hazards of man's right knowledge. "A poet," he tells us, "needs to keep his wilderness alive inside him," seeking his "darkest Africa." The pursuit of dangerous places takes Kunitz through several poetic incarnations. His verses go from dense and highly figured to almost transparently clear. The Platonic abstractions of a young man experiencing mostly Intellectual Things -- as Kunitz aptly titled his first volume -- mature into poems firmly fastened to the realities of our day. Kunitz relies increasingly on a mix of memory and immediate observation to trigger his poetic discoveries. He perceives universals in minute particulars, and his loving attention to detail is telling, whether he is showing us a dragonfly beaten by the rain -- "scales, tortuous wires, / flakings of green and gold" -- or a small bird wounded: . . . when I held him high, fear clutched my hand, for through the hole in his head, cut whistle-clean . . . I caught the cold flash of the blue unappeasable sky.

The verses can seem relentlessly grim. In the suburbs trees are pulled from the dwindling green patches of our environment: "All day the hireling engines charged the trees,/Subverting them by hacking underground." In Germany Dietrich Bonhoeffer, graced by conscience, takes his last steps toward the hangman at the Flossenburg extermination camp. Yet Kunitz offers "Signs and Portents" of both pain and possibility. Throughout the volume we explore with him the depths of his own being, and find there, even in "darkest nights" when the poet "roamed the wreckage," the promise of life energies renewed. Like his old man "Solomon Levi" Kunitz will continue to "dance for joy of surviving, / on the edge of the road": Though I lack the art to decipher it, no doubt the next chapter in my book of transformations is already written. I am not done with my changes.

While Kunitz's art has changed with the years, his preoccupations and themes have not. The epigraph for his first book marked the path clearly: "For the tear is an intellectual thing." Mind and emotion cannot be separated whatever the difficulties of their interweaving. Those who are moved by this thought can only be grateful that both Kunitz and Warren continue to affirm in their art the unity of all experiences.