The No. 1 choice of pop-music divas

The moment that R&B; newcomer Rihanna shot to the top of the Billboard Hot 100 chart earlier this month with her bootylicious new single, “SOS,” producer Jonathan “JR” Rotem’s phone started to ring off the hook.

Already a platinum hit-maker in his own right, Rotem forged his reputation crafting bass-heavy beats for a who’s who of hip-hop’s elite -- 50 Cent, D12, Snoop Dogg and Mobb Deep among them. But after producing “SOS,” interest in the South African-born, Bay Area-raised producer has been coming from a wholly different quadrant of the celebrity universe.

Suddenly, Us Weekly’s favorite bubble-gum divas, Paris Hilton and Jessica Simpson, are booking studio time with him.

“It’s weird how it goes from hard-core rap to as-pop-as-you-can-get like that,” Rotem said. “I always wanted to do all kinds of music. You can’t control the cycle.”

But you can almost predict it. Pop music’s producers du jour are the newest intimates of Hot Young Hollywood (insofar as Hilton, Lindsay Lohan, Hilary Duff and Ashlee and Jessica Simpson can be said to personify psychic-geographic terrain).

In an effort to make their voices as culturally relevant as their marquee value, the ingenues rely on a small pool of behind-the-scenes writer-producers such as John Shanks, Kara DioGuardi, Lukasz “Dr. Luke” Gottwald and Rotem who boast platinum-plus track records and industry bona fides.

Moreover, Hilton and Simpson join Britney Spears to round out the holy trinity of tabloid mainstays with whom Rotem is currently at work. Spears quietly enlisted the producer for her comeback album after hearing “SOS” (“She told me flat out, ‘I love that song,’ ” he said.) And since first meeting in Las Vegas in March, they have cut four rough tracks together at her Malibu home studio.

“I am flattered that artists such as Jessica Simpson, Britney Spears and Paris Hilton are inspired by the success of ‘SOS,’ ” Rihanna said. “I am certain [they] will have much success by working with him.”

Rotem worked with Spears as recently as last week and said her newly announced second pregnancy hasn’t affected the pop tart’s creative output so far.

“She’s focused and that part of it doesn’t get in the way of what she’s doing,” he said. “And even though she’s so young, you could feel that you’re in the presence of a veteran of performing who can get in her zone and knows what she wants to say.”

A classically trained jazz pianist who originally aspired to score film soundtracks, Rotem recently previewed several of Spears’ new songs for a reporter.

On the club banger “Everybody” -- that borrows liberally from an ‘80s mega hit in much the same way “SOS” is structured around a recognizable chunk of Soft Cell’s “Tainted Love” -- Spears croons about carnal desire and dance floor bump ‘n’ grind in a breathy lower register. But she shifts gears for “Who Can She Trust,” an introspective composition the producer says Spears wrote herself. Over a “snap music” hip-hop beat accompanied by the sound of a camera shutter clicking she sings, “Where am I?/ Where will I find my face?/ Where will I find my faith?”

As if the Berklee College of Music graduate’s client roster didn’t already read like the under-25 Celebrity Stock Exchange, Rotem is also collaborating with Spears’ husband, Kevin Federline, and has made a pet project out of altering the Ferrari-driving former backup dancer’s negative public image.

Their first joint effort is K-Fed’s braggadocio-laden rap track, “America’s Most Hated” -- a song that’s been streamed nearly 270,000 times on Federline’s MySpace.com Web page.

Federline raps, “I got 50 mil, so I can do whatever I want,” on the track. “All that [expletive] rappers talk about, I already did it, I got my name spreading faster than crack.” And during a piano interlude between verses he says in a slurry, drunken-sounding voice, “We are gonna go swimming with women!”

“I met him and just genuinely liked the guy,” said Rotem, shoeless and seated on a black leather sofa in his Century City home studio. “You hear a lot of things out of context, so I didn’t know what to expect. But he seemed genuine and warm and not how he was painted to be. We established a friendship very quickly.”

“I think he’s a good person and talented,” he continued. “When he delivers lyrics, it’s entertaining.”

Federline makes it clear that the feelings are mutual.

“When we get together in the studio, he makes sure to create an extremely comfortable environment which allows me to open up and express my feelings in order to produce an amazing song,” K-Fed wrote in an e-mail response to a request for comment. “In my eyes, he’s an A-plus producer and a beast when it comes to putting together masterful beats that are unique to each artist he works with.”

Rotem got his big break when one of his beats wound up on Destiny’s Child’s 2001 multi-platinum album, “Survivor.” But despite a strong pop debut, he quickly moved into the hip-hop arena; rap supremo Dr. Dre hired the producer to make beats for his highly anticipated album “Detox.” And in the last month, Rotem’s songs for 50 Cent, “Best Friend (featuring Olivia),” and Lil’ Kim, “Whoa” (which also is the theme song for the rapper’s upcoming reality TV series), have cracked hip-hop’s Top 40.

“It’s all about showing the artist in the best possible light,” Rotem said, running his fingers along his signature piece of jewelry, a diamond-encrusted keyboard dangling from a chain. “It’s a partnership. You have to stop seeing them as a famous person rather than a person who’s trying to make the best possible music.”