The artist stands at the top of the scaffolding; the man who hired him is at the bottom. "It should be done by now."

"Tomorrow," deadpans the artist. The wall behind him is nearly blank.

"No, seriously, how long before it's done?

"Six months," shrugs the artist.

"Six months?"

"Five months . . . four months." He thinks for a second. "Seven months."

Do not try to hurry Alexandru L. Mazilescu. He is a 74-year-old Romanian refugee - one of the few artists in the United States, in the world perhaps - still qualified to paint a traditional Byzantine icon of the Madonna and Child on the 35-foot-high apse behind the altar of St. Nicholas Greek Orthodox Church in Queens, N.Y. And he works only one way and at only one pace: his.

He is a perfectionist. He sketches his basic designs 200, 300, sometimes 400 times before he is satisfied. Then he makes a model for his sketches, then larger sketcches from his model, then a larger model from those sketches, then more sketches - many more sketches - on the wall itself before he will begin to paint. The models are exact. "I don't understand this old man," says Rev. Constantine Volaitis, pastor of the church. "He's beyond me. Look at this." It is a model Maziluscu rejected for the apse that is so good Volaitis keeps in his office. "And to get this took a couple of hundred shots.

Volaitis thinks Mazilescu is a genius. So does the Rev. Spyridon Macris, pastor of the only other church in the United States as Mazilescu has done, Holy Trinity Greek Orthodox Church on Staten Island. "I love him as dearly as a father," he says. "He's a great man." He's also very frustrating. "The only sure thing about Mazilescu is that his time schedule is not to be held to," Macris says "He feels a time schedule puts pressure on it. I've seen him walk off a job for a couple of weeks because the inspiration was not there . . . But when he's got his ideas, when he's inspired, he'll go three or four days without sleep, continuously working as the spirit moves him."

It took Mazilescu three years to paint the apse and the dome of the Staten Island church; he is to paint both the apse and the dome in Queens as well as seven side panels below the 75-foot-diameter dome. No one knows how long it will take. "Whatever commitments Mazilescu makes," Macris says, "I warned Father Volaitis not to take seriously."

Mazilescu is beginning with the Madonna and Child, traditional subjects for the Apse in a Greek Orthodox Church Two brothers - Sophocles and Mingo Logothetis - have pledged $30,000 for the mural in memory of their parents. And a fund drive is under way to raise money for the rest of the project, the total cost of which will be more than $100,000.

Mazilescu designed the mural, which was submitted to a church committee for approval. There was little for the committee to decide, Volaitis said. "By the time he showed it to the committee, what was there left for us to say? 'Go ahead.'"

The mural will have the Madonna and Child seated on a bench-like throne. The style, Mazilescu said through an interpreter, will be "modern Byzantine, interpreting in a modern way the old Byzantine." The old Byzantine calls for angels at her side, but Mazilescu "doesn't like the idea"; and in his painting, her feet point downward, a departure from the old way, which usually kept the Madonna's feet inside her dress.

Mazilescu has literally moved into a small room off the nave of the church where he has neatly laid out a small bed, three artists' tables, a television set, his supplies and several of his paintings. Volaitis calls him "our artist in residence," but Mazilescu, who speaks little English, says through his assistant-interpreter-secretary Denise Janco that he stays there overnight only when the painting itself begins.

Mazilescu signs his paintings and drawing with the acronym ALM - his initials, he says that for him his paintings is art, not religion; but Violaitis disagrees. Iconography is religion, he says, "and I'm fairly convinced he's the greatest of the icongraphers living today."