HIS SEA-BLUE eyes glistening, Theodore Bikel says he has waited his entire life for this role: "I've played kings, I've played murderers, I've played all manner of savory and unsavory characters." He was Broadway's original Captain von Trapp in "The Sound of Music," for one, and has also taken on Shakespeare's King Lear, among the thorniest roles in English-speaking theater. The actor who plays the aging and misguided monarch, doomed by his own bad judgment, needs both physical and emotional fortitude. Theodore Bikel has played his share of Lears.

But Lear, Bikel says, is nothing compared with the 12th-century Spanish rabbi and Talmudic scholar Rabbi Moses ben Nachman, the central figure in Theater J's "The Disputation." Hyam Maccoby's drama, set in a medieval Spanish courtroom, pits Nachman against a Dominican monk who has converted from Judaism during the Spanish Inquisition. Bikel calls the play "a mammoth undertaking" and one steeped in controversial issues, among them the theological roots of anti-Semitism and the psychology of guilt and blame.

Bikel, perhaps best known for his portrayal of a less learned, though no less endearing Jewish icon, Tevye, the comic philosopher of "Fiddler on the Roof," is ecstatic about taking on the mantle of a rabbinic scholar. Playing Tevye, which he has done more than 2,000 times around the globe, was easy, he says -- he just channeled his grandfather. The issues informing "The Disputation" also brought back memories of Bikel's Viennese childhood in the years before World War II, where even as a young boy he was tutored in the Bible, Hebrew and the rudiments of the Talmud.

At the time of his death in 2004, Maccoby was an internationally acclaimed British scholar of rabbinic history who delved deeply into centuries-long issues in Jewish-Christian relations. The Barcelona Disputation of 1263 -- an actual debate between Nachman and monk Pablo Christiani (Edward Gero) -- formed the basis for "The Disputation," which dissects the fundamental theological differences between the two religions.

But Bikel, who speaks five languages, insists that Maccoby's historical drama is neither dry nor scholarly. "The play," says the actor, "is surprisingly modern, and a lot of it is also surprisingly humorous, because you can't engage in verbal fencing without some wry humor."

And verbal fencing stands at the center of "The Disputation." By the time Bikel's character -- also known as Nachmanides -- was called on to defend his beliefs and those of his Jewish compatriots, the Inquisition was well underway, its goal to either convert or eliminate Jews from Spain. These public tribunals were anticipated and attended like sporting events today, but with life-or-death consequences.

"You try to be as truthful, as sincere and as honest as you can," Bikel says, whose Rabbi Nachman faces his disputant and meets a measure of his own theological truth: "For this role there are hoops that you have to jump through that are of a dialectic nature. . . . This is an intense intellectual exercise. It also takes leaps of faith. On the outcome of this disputation hung not just the fate of Rabbi Moses ben Nachman himself, but also . . . the entire Jewish congregation."

Theodore Bikel, right, plays the 12th-century Spanish Rabbi Moses ben Nachman and Edward Gero is the monk Pablo Christiani in the religious drama "The Disputation."