NEW YORK – If you want a sense of how stressful it’s been for 50 Cent to release his third album, just look at the CD cover.

Whereas his first two albums featured portraits that exuded confidence and authority – a rippling torso coupled with a menacing glare – 50’s new album out Tuesday, “Curtis,” shows a seemingly frustrated 50, hands on his head, an extreme close-up accenting his furrowed brow.

“This has been such an unpleasant process,” 50 admits during an interview, a bit wearily.

At times, it’s been a downright unfriendly process as well. First he had to deal with a lackluster response to the album’s first singles, including the “Candy Shop” sound-alike “Amusement Park” that drew yawns from radio. Then his record label, Interscope, pushed back the release date from summer to fall amid battles over promotion.

Finally, there have been whispers – getting louder by the day – that the streets are growing tired of their favorite bullet-scarred, tough-talking antihero. A direct challenge from critical darling Kanye West, whose album “Graduation” also drops Tuesday, only served to fuel rumors that the mighty 50’s global empire is vulnerable.

Still, despite all the setbacks, 50 isn’t about to cede his position as rap’s reigning sales king, to Kanye or anyone else. When asked if he’s suffering from a backlash of sorts, he readily acknowledges it – and just as easily dismisses it.

“That’s exactly what I’m experiencing. Like right now, they’re anti-Beyonce,” he says of hip-hop’s fickle fans. “But we don’t have a replacement for Beyonce. … and we don’t have a replacement for 50 Cent. Until they can find an artist that builds the same consistency … they better stick with what they got before they be stuck with nothin’!”

Given 50’s past spectacular success, it’s hard to fault his bravado. He debuted in 2003 with “Get Rich or Die Tryin’,” which sold a stunning seven million copies. Two years later, his “Massacre” sold 1.1 million the first week alone, and went on to sell approximately five million.

His victories didn’t stop at records. The charismatic New York rapper launched a G-Unit record label, which had top selling debuts from entourage members like Lloyd Banks, and G-Unit clothes, which have adorned everything from baby tees to backpacks. He also became a mogul with deals like a Vitamin Water endorsement and street lit book franchise, and starred in several movies, including his own autobiographical flick.

“He’s transcended just rap or hip-hop,” says Stephen Hill, an executive vice president at BET. “He’s a businessman, he’s head of a G-Unit brand … He’s incredibly smart as well as being incredibly connected to the street.”

But the run-up to “Curtis” hinted at his first possible stumble. This spring, the singles began to hit radio – but they did not become instant hits, or hits at all. “Straight to the Bank” and “Amusement Park” never resonated with fans and were considered disappointments – though in 50’s eyes, they were still successes.

“It’s tough, because when I release records that they would consider a hit record for another artist … for me they go, ‘it was a lukewarm response,'” says the rapper as he sits in a huge Manhattan loft that serves as a showcase for his G-Unit apparel.

“In the history of entertainment, they build entertainers in order to destroy them, I think they were giving me resistance period.”

Yet later, in the rare admission of a misstep, he says: “I guess it’s just timing. … I had the records, I just launched the wrong ones at the wrong time.”

The single “I Get Money” is turning out to be the right single at the right time. The street anthem has garnered a huge buzz, even if it hasn’t been a massive radio hit yet.

“This is the song that has connected, this is the first song that he’s put out that has gotten the reaction that he expects from a 50 record,” says Hill. “If you’ve been in a club when it gets on, if you’re not headed to the dance floor please get out of the way, because there will be a stampede.”

50 is looking for a similar reaction in record stores. To that end, the album is jam-packed with mainstream pop artists, a first for him, including collaborations with Justin Timberlake, Robin Thicke, Mary J. Blige and even Nicole Scherzinger from the Pussycat Dolls. Looking at those names on a 50 Cent disc, some might wonder whether the man whose trademark is gritty anthems punctuated by the sound of gunshots had gone too pop.

50 understands the concern, but says such fears are unfounded given the presence of such songs as “My Gun Go Off,” “I Still Kill” and “Fully Loaded Clip.”

“If you went just by the features you would think this is a total different record, you would think it was an R&B; record, but … it still has the aggressive content you would expect from a 50 Cent record, it’s just done from a different context,” he explains. “Creatively I’m in a space where I’m secure enough to try something different.”

While it may be a creative departure, in many ways it’s commercially calculated. When he talks about his collaboration with Thicke, rather than discuss it musically, he plays up reaching a different commercial audience that’s actually buying records. Ever the businessman, 50 strategizes about the dwindling recording industry and how he’s adjusting to an imploding market: “I don’t think I can ever actually, legitimately have expectations of selling 12 million records again, and that window is closing as we go,” he says with a chuckle.

But as long as he continues to put out records, he still expects to be king.

“I think I’ll be on the roof based on whatever the possibilities are based on the consistency of the material I’ve delivered from the past up until this point,” he says. “There ain’t nobody else (for me to) actually compete with.”