NEW YORK — "So you'll step down there," the stage manager calls out, "and zoom! You meet your kids."

Fantasia steps forward gingerly and hugs two kids before turning around and proclaiming, "Wait! This one ain't mine!"

Of course, she's joking — neither of the two actors during this rehearsal are her "kids," anyway (they're both understudies). But throughout her first run-through rehearsal for "The Color Purple," whose cast Barrino joins on Tuesday, the "American Idol" winner has been working to relieve the tension in the air — cracking jokes, busting out improvised dance moves and making light of any mistakes she makes.

(Get behind the scenes of Fantasia's first rehearsal, plus see previews of three of her show-stopping songs.)

It's more tense than usual because most stars of Broadway productions rehearse for weeks before they take the stage. But not Fantasia, who came down with strep throat when she arrived in New York, which meant spent most of the past week forbidden by her doctor from talking, let alone singing. And now, on her first full day of rehearsal, opening night is just six days away.

"I started to cry," Fantasia explains. "And the doctor was like, 'What are you crying about?' I was like, 'Doctor, I have work to do. I have a big position!' But all the [previous] Celies told me they got sick before they went on, so I think it was just nerves."

(Check out photos from the rehearsals right here.)

Oprah Winfrey, who produced the musical, and lead producer Scott Sanders handpicked Fantasia to play the part of Celie (see "Living 'Color': Fantasia Tells Oprah She's Already Learned From Celie"), a meaty role that has won LaChanze, the Broadway actress who originated the role, a Tony Award, and also snagged Whoopi Goldberg, who did the movie version, an Oscar nomination. Celie is "poor, black and ugly," as the Mister reminds her — the Mister being her husband through an arrangement that's more rape than marriage (occurring after the man she believes to be her father has already "spoiled" her with two children by the age of 14).

Celie endures trauma after trauma -- abuse, incest, beatings -- but through her relationships with Shug Avery, the Mister's mistress, as well as daughter-in-law Sofia and sister Nettie, she finally shifts from enslavement to empowerment.

"When Oprah came to me and said, 'We think you're Celie,' I was like, 'Me?' " Fantasia recalls. "You think I'm Celie? You never saw me play the part.' And she was like, 'When we look at your story and the things you talk about, we think you're our Celie.' When I watched the movie growing up, I thought Shug Avery was the bomb. But I always like to say, when I sing songs, I can't sing anything I can't relate to. And I relate to Miss Celie. She went through a lot of things I went through, but she came out a strong woman. And so did I."

Given that both Whoopie and LaChanze played Celie to great acclaim, Fantasia is working hard to make the part her own -- to be believable as a black girl who grows up in the rural South in the early decades of the 20th Century, who doesn't know how to stand up for herself.

"I'm freaking out [right now] — you just can't see it," she says. "It's a lot of responsibility to be in a show that's been running two years now, and everybody else had a chance to get comfortable in their parts — Miss LaChanze really put her stamp on it. So here I have to come out there and just carry the show. It's a lot of pressure. It's different from getting out there and just singing, because I can do that all day long."

Still, she has to practice the lyrics, so she holes herself up with the show's musical director Linda Twine and arranger Joseph Joubert in a small room with just a keyboard to go over how to enunciate properly for the theater. "Breathe," Twine frequently reminds her. "And exaggerate that phrase more."

Fantasia resumes singing: "No time for my read-ing, no birds gonna sing/ No time for my read-ing, I sang the wrong words." They laugh, and Twine gets her back on track, "It's a solo — you've got to spit it."

After the songs, Fantasia has to find her footing — literally. She dances in just two numbers, so most of her blocking addresses where she should walk and stand during scenes, which is trickier than it sounds because part of the stage moves. "You have to know where to be so you don't float off," Fantasia laughs. "They have numbers on it, but it's odd if you're looking down during the performance, so you have to just get it in your head. That's the hardest part."

Of course, the hardest part is even more complicated during rehearsal because they don't have the full set — so Fantasia keeps "bumping into" things that aren't there. "I know you're missing a few spots," the stage director says, laughing, "but you'll have more perspective once everything is onstage."

Perhaps, but a fuller set means fewer opportunities for jokes: Fantasia teases Angela Robinson, the understudy playing Shug Avery, "Oh Angela, you're the best kisser I've ever had!"

Everyone laughs. But later, more seriously, Fantasia insists, "It's no joke. At first I thought this would all be a piece of cake, but it's hard work. I'll probably forget everything the day of — I'll probably be in the bathroom all day with my nerves! I'll be running around like a chicken with its head cut off.

"But wow," she sighs. "I'm going to do Broadway. That's crazy!"