On Easter Sunday, CBS will tell the story of what some people in Santa Fe, N.M., believe to be a miracle: the construction of an unsupported circular staircase in the Sisters of Loretto Chapel by a mysterious carpenter who, upon completing the job in about 1878, disappeared without collecting his pay.

The actual coiled staircase, which makes two turns between the Gothic chapel's floor and its choir loft, is made of wood that is still unidentified. Built without nails or center support, it is an engineering and architectural wonder that attracts thousands of visitors each year. Its railing was added later.There are those who believe that the lone carpenter, who used only the simple woodworking tools avail-able to him, was an incarnation of an earlier carpenter, perhaps the one whose return from the dead gave Easter its meaning, or maybe his earthly father, Joseph, also a carpenter. They believe it was not coincidental that the 22-foot-high staircase has 33 steps - Jesus' age at his death.

To screenwriter Christopher Lofton, it's also something of a miracle that, after two decades of trying, "The Staircase" finally got produced. His conclusion: The time was right, finally.

Lofton's story begins as Mother Madalyn, played by Barbara Her-shey, inspects what she believes is a completed chapel only to find that the architect and builders have not constructed a staircase to the choir loft.

So the nun, who is dying, gathers her sisters to offer a novena, nine days of devotions and prayers to St. Joseph, patron saint of carpenters. On the last day of the novena, a stranger with a donkey and tool chest appears out of the desert and offers to build the staircase that no one believes can be constructed in the chapel's limited space.

William Petersen plays the carpenter, Joad, who teaches the headstrong, Irish-born nun a few things about faith, even as he understands her overwhelming desire to get the chapel finished before she dies. Diane Ladd plays Sister Margaret, a more-traditional nun who is sometimes unsettled by Mother Madalyn's irreverence, although the two women share a strong bond.

Screenwriter Lofton, who studied civil engineering at the University of Michigan before becoming an actor and a writer, said he became fascinated by the Santa Fe staircase after reading about it in a magazine. Thinking of writing a script, he began to search for information about the real Sisters of Loretto who traveled from Kentucky, where they were based, to New Mexico to teach, at the request of the territory's bishop.

Lofton acknowledged that because information was sketchy, he created the relationship between Mother Madalyn (in real life, Sister Magdalene) and the carpenter, whom he called Joad, to add a human element to a story that is more about the lessons the nun has to learn than it is about the staircase.

"This is somebody who really had her heart in the right place," he said. "She wanted to finish this chapel as thanks to God. But she's running out of time and money, so her human desire to get the thing built takes over. Mother Madalyn could have said, `I've done everything here and this isn't working out and I don't have enough time or money.'

"What Joad does in life is try to help people," he continued. "It's not glamorous, not something that he necessarily expects to be paid for. He doesn't care much about his personal happiness. And he doesn't come to instruct Madalyn on faith. This man, who has a little bit more patience or spiritual wisdom, this man has devoted his life to helping people."