I’m 21 years old!

Most young men can only dream of getting breathless phone calls from Jennifer Lopez. But when the screen siren-turned-singer’s first single, “If I Had Your Love,” reached No. 1 on the pop charts last month, she immediately dialed the number of Rodney Jerkins.

“She called me and said, ‘We’re No. 1! We’re No. 1!’ ” recalls Jerkins, who produced and co-wrote Lopez’s hit. “I just said, ‘Didn’t I tell you?’ ”

If Jerkins sounds blase, even cocky, he has reason to be.

This pastor’s son is among the hottest songwriter-producer-arrangers in contemporary R&B.; Over the past year, Jerkins has also crafted or helped build hits for Whitney Houston (“It’s Not Right, but It’s OK”), and Brandy and Monica (the Grammy-winning duet “The Boy Is Mine”).

Jerkins is now working on tracks for Michael Jackson’s comeback effort, due this fall, and for salsa star Marc Anthony. He will work with the Spice Girls and LeAnn Rimes later this summer, and is also scheduled to collaborate with Will Smith, Puff Daddy and Toni Braxton on upcoming projects. And Jerkins is developing new talent for his own label, Darkchild Records, for which he signed a deal with Sony Music in January.

Not bad for someone who just turned 21.

Thomas D. Mottola, Sony Music’s chairman and CEO, is among those impressed by the young phenom.

“He has been delivering great things for us at Sony,” says Mottola, whose roster of artists includes Jackson, Lopez and Anthony. “Rodney has a much broader vision musically than most of the young producers who are up and coming. . . . I think he’s just at the beginning of where he’s going to end up.”

Adds Jerkins’ fellow New Jersey denizen Houston: “His musical background, his church upbringing and his family heritage make him one of the premier producers today. I love that dark child!”

‘I Work More Than I Sleep’

Jerkins is so busy these days that he built an apartment over his Darkchild Studios complex--a converted warehouse here, near his hometown of Galloway, a suburb of Atlantic City. The structure also houses offices for Darkchild Records.

The cherubic prodigy, who still lives with his parents, wanted a bedroom on the premises--not that he has much use for it.

“I work more than I sleep,” he says, lounging on a couch in one of his recording studios during a rare break. “My average workday is 16, 17 hours. Sometimes we’ll go 20 hours straight, sometimes 24. And I work seven days a week. I try to take off Sundays from noon to 3 or 4 so I can go to church . . . and sometimes I’ll take off two hours to shoot pool or go bowling. But then it’s back to work.”

When people ask how he maintains such a schedule, he tells them, “I’m 21 years old! I’m supposed to have this energy! If I wasn’t doin’ this, I’d be out partying and actin’ a fool. I might as well make some money off my energy, you know?”

Jerkins attributes his daunting work ethic to his father, a Pentecostal minister who now manages him, and his mother, who directed the church choir.

The youngest of four siblings, Jerkins began studying piano as a young child. At 9 or 10, he began sneaking into the room of his big brother and tinkering with his keyboards and drum machine. (The brother, an aspiring musician and producer himself at the time, currently collaborates with Jerkins; his two sisters also work for him, one as a personal assistant and the other as a Darkchild Records executive.)

After discovering the music of rapper Slick Rick and the seminal hip-hop/soul outfit Guy, Jerkins started dreaming of a career in production. His parents, who preferred that their children listen to gospel music--”I had to hide my cassettes,” Jerkins says--were initially wary of his ambitions. But Jerkins convinced his father that he had found a calling: “I told him, ‘I think I have a gift. Everybody has a special thing, and this is mine.’ And he got behind me 100%.”

Jerkins began working professionally at 14 and got his big break the following year, when a demo he had recorded with some Atlantic City bands was passed to his idol, Teddy Riley, Guy’s driving creative force and one of modern R&B;’s most influential writer-producers.

After Jerkins heard that his tape had impressed Riley, the young upstart got his father to drive him to Riley’s studio in Virginia.

“We waited in his parking lot, and then I rushed his car,” Jerkins remembers. “He said, ‘Come on in!’ He put me on a piano and we played music for like three hours straight. On top of that, he told a lot of people about me. He said, ‘There’s this kid comin’ up.’ ”

With Riley’s support and encouragement, Jerkins began to find work with young acts. In 1995, he signed a worldwide deal with EMI Music Publishing. Two years later, he scored a major coup by contributing five songs to Mary J. Blige’s multi-platinum album, “Share My World.”

Other artists who have benefited from Jerkins’ pop-soul savvy include Kirk Franklin, Aaliyah, Deborah Cox, Luther Vandross, Tatyana Ali, Shaquille O’Neal and Brian McKnight.

“I have to turn down a lot of calls,” Jerkins says. “But if there’s somebody I really want to work with, I’ll just go for it. Like right now, I really want to work with Celine Dion. So I’m about to take a day out of my schedule to focus on writing something really great for Celine.”

Jerkins is so in demand now that his wish list includes a number of artists outside the R&B; arena, from the rock band Aerosmith to country behemoths Garth Brooks and Shania Twain. “I don’t want to be narrowed down to just R&B;,” Jerkins stresses. “If I can write a hit song for Garth Brooks or Aerosmith, then I’ve proven myself in another field.”

Teen diva Monica thinks Jerkins can expand into new areas.

“I see [Jerkins] becoming very diverse and universal, producing various types of music,” she said in a separate interview. “He’s open to others’ ideas . . . and he keeps new ideas coming.”

Hopes to Branch Out Into Filmmaking

Jerkins’ most thrilling accomplishment to date has been his ongoing work with Jackson.

“Michael Jackson was my biggest wish ever,” he says. “He’s pushed me more than any artist or record company. We had a lot of fun; I’d play the music real loud and we’d go crazy--pumpin’ fists, clappin’, cheerin’. His drive is unbelievable. He would call me at 5 in the morning, in the studio, and I’d be like, ‘What are you doin’ up?’ And he’d say, ‘I just want to make sure everything’s goin’ right.’

“There’s a lot of pressure, working with a Michael Jackson or a Whitney Houston. There’s no two or three pitches--if you miss once, you don’t get a second chance.”

Such creative pressures are compounded by Jerkins’ new role as record company CEO. He has already signed two acts to Darkchild Records--the girl-group Plush and singer Rhona Bennett, whom Jerkins describes as “on the same line as Whitney or Mariah [Carey]. She’s [going to be] that big a star.”

Jerkins also hopes to branch out into writing, directing and producing films. “If you’re a writer, you shouldn’t limit yourself,” he reasons. “What makes a great song is a great story--making drama happen. If I can take that and turn it into a movie or even a TV show . . . I think that’s my next move.”

You probably won’t catch Jerkins in front of a camera, or behind a microphone. Although he recorded a contemporary gospel album in his early teens, Jerkins insists, “My thing is to be behind the scenes, creating the star . . . or taking the star to another level.”

In these pursuits, Jerkins feels his potential is virtually unlimited. “If I ever retire, I want to do it while I’m hot,” he says. “That’s the scary part of being so young. . . . Sometimes I think, ‘Am I still gonna be hot when I’m 28?’ But I think I will be. I feel like I’m at the top of my game right now, and I’m hopin’ to stay there for a long time.”