If the Brill Building still were the songwriting hub it once was, Bruno Mars would be both guarding the entrance and occupying the penthouse suite. Not only is he probably the best pop-oriented traditionalist songwriter of the past five years, he's also the one who's been most successful at preserving that practice in the mainstream. Others are more daring, their songs taking unanticipated left turns or staying in the high-minded conceptual clouds. But no one brings it home quite like Mars, a model of concision who always knows where the trigger is - and always, always pulls it.

Take "When I Was Your Man," from his impressive new second album, "Unorthodox Jukebox" (Atlantic), which follows his excellent debut album, "Doo-Wops &amp; Hooligans," from 2010. This song opens with piano, dark and struck hard, a sad theme being resolved. But then things lighten, and Mars begins to sing:

Same bed, but it feels just a little bit bigger now,

Our song on the radio, but it don't sound the same.

When our friends talk about you all it does is just tear me down,


This is succinct writing, a little talky but extremely conscious of the borders. It could work on the radio. It could work on Broadway. It could work in a jazz club. Mars builds a sturdy skeleton.

If the muscles atop it are sometimes too lean, well, that's both Mars' calling card and his crutch. He has a feathery tone, and though he's deceptive with his power, he is not a powerhouse. That's why on this album, on songs when he wants to grab attention, he emphasizes a particular style or influence.

"Locked Out of Heaven" is a vivid carbon copy of "Zenyatta Mondatta"-era Police, and "Show Me" is a lovers'-rock reggae song that recalls UB40 (and is one of the highest-profile pop productions by Supa Dups, who worked on the track) and the Flamingos' "I Only Have Eyes for You."

"Treasure" evokes the disco and funk bands of the mid-1970s, and "Money Make Her Smile" is cribbing notes from Michael Jackson's "Dirty Diana." The finish to "Gorilla" is a heavy-breathing blend of Prince, Corey Glover and gospel.

The new album flies by quickly - 10 songs in 35 minutes - sure of its mission. And its songs, which span light rock, light R&amp;B and light pop, are exceptionally drawn and lush, produced largely by the Smeezingtons, the collective of Mars, Philip Lawrence and Ari Levine. They're helped on several songs by Jeff Bhasker, who has worked with Kanye West and is best known for giving the rock band fun. a pop booster seat that recently resulted in six Grammy nominations. Emile Haynie worked on a few songs, too: He's best known for his work with Lana Del Rey.

Those combinations make sense: These are some of the most energy-infused but profoundly cosseted songs you're likely to hear all year. They are sturdy cages designed to protect Mars while attracting onlookers.

That's because his backbone is still forming. Mars has a Zelig-like talent for fitting into different sorts of sounds but not a chameleonic one that lets him change his fundamentals. He got his start writing songs for others and then slowly established himself as a go-to hook singer in an era when hip-hop was becoming decentered, suburbanized and shot through with crisp melodies. He is a sideman made good.

And also a solo star, even if his songs sometimes suggest ones that might be made by other more emphatic, stylistically unique singers.

With that in mind, maybe it's not too soon for a Bruno Mars tribute album, in which other singers give a glimpse of pop songs that could have been. How would "Unorthodox Jukebox" sound if the songs sought out higher ground?

Herewith, a thought experiment:

"Young Girls": This song swells something serious, heavy drums pounding as a counterpoint to the ascendant melody. The ambition is undeniable. If it were 1982, this would call for Bono and U2, but in 2012, try Daughtry.

"Treasure": This features Mars' lightest singing, but the reference points are louche. Ke$ha would take these innocuous words with the naughty undertones and ferret out their bawdy center.

"When I Was Your Man": The piano tells it all on this song, which is one of the most certain on the album. If this isn't the beginning of the Billy Joel comeback, people should lose their jobs.

"Natalie": It's unsettling to hear Mars' incensed side on this song about chasing down a woman who robbed him; he's far too tender for the task. Better hand it off to someone such as Eric Church, who starts growling before breakfast and doesn't stop until after the night's last whiskey.

"Money Make Her Smile": Mars' trip to the strip club - "Coming to the stage is a girl who's new in town/ She go by the name Where Your Stacks At" - is him at his most serrated and anguished. Drake would loosen the song up while keeping its pathos intact.

"If I Knew": The album ends on this beautiful, pure doo-wop song, a reminder of Mars' classicist roots and a chance for his voice to roam free. Only another classicist could do it justice: Tell Jack White to strap on a guitar and step to the microphone.