MUSIC : The Jones Phenomenon : Return of The Voice may defy reason, but it’s back--and fevers are on the rise again.

The task I set myself was this: To plumb the Tom Jones phenomenon.

Because, frankly, I don’t get it. Tom Jones--yes, the same Tom Jones who sang “It’s Not Unusual” and got pelted with push-up bras and room keys--is not just back, he’s back with a large and growing audience of people young enough to be the children of the lingerie tossers. Hell, I’ll go out on a limb here and say some of them actually are the children of the Victoria’s Secret hurlers, children who are all grown up now, or at least big enough to see over the counter at Tower and buy their own music.

It is this hip and happening Tom Jones, the Tom Jones as well known for his cover of Prince’s “Kiss” as for “Delilah,” who will appear tonight at the Universal Amphitheatre.

But if the cover photo on his new CD, “The Lead and How to Swing It,” is any indication, the new Tom Jones and the old are one and the same. There he is, wailing his famous microphone-destroying wail, in a fishnet T-shirt and what look remarkably like Sansabelt slacks.

A fixture of golf courses everywhere, Sansabelt slacks are not surprising on a 55-year-old guy, which is what Jones is, unless the guy happens to have a reputation as a sex symbol, which Jones also has. And not even the grunge crowd, who will wear whatever it takes to induce that “Where’s-that-bad-smell-coming-from?” grimace on their parents’ faces, have been known to resort to Sansabelt.

So I ask you, what’s the deal? Has the youth of today forgiven Jones for “What’s New, Pussycat?” or have they simply never heard it?

For answers, I turn first to the press kit provided by Jones’s new label, Interscope Records. The publicist’s bundle includes photos of Jones looking enviably fit (he does crunches, I learn) and selected reviews of his recent concerts and club dates. Unfortunately, the latter are about as illuminating as Alan Greenspan on the economy. I am still trying to figure out what critic Charles Taylor meant when he wrote in the Boston Phoenix: “Treating Tom Jones as if he were camp reinforces the prissy notion that great pop is about authenticity.” Huh?

More perplexed than ever, I approach one of Jones’ new fans. West Wheeler, 24, of Burbank is a musician himself, a drummer with an alternative band (actually a power alternative band) called Shoot the Moon. Wheeler would go to a Jones concert in a New York minute, he says, explaining, “I don’t own any Tom Jones, but I really like him.” But why? I press. And Wheeler offers several hypotheses: Jones’ old stuff is “fun and bouncy,” “people have made fun of him so long he’s cool,” and, probably closest to the mark, Jones has, through his gutsy interpretation of contemporary material, managed to stay fresh.

Still questing, I call free-lancer RJ Smith, who writes as insightfully about music as anyone I know. When Jones was at the House of Blues recently, Smith reports, “every indie rock band in town was trying to scam their way onto the guest list.” Skillful packaging has helped recharge Jones’ career, says Smith, noting that the photos on the new CD are by hip fashion photographer David LaChapelle. As to what is packing in the young fans, Smith is willing to speculate: “It’s just so hard to find good Martian music these days.”

Music business types are next. David McLees, who produces compilations for Rhino Records and keeps a close eye on the reissue market, attempts to explain it all for me. McLees reasons that what today’s youthful fans relish most about Jones is that their baby-boomer parents didn’t like him and their grandparents did.

Today’s young consumers are aficionados of pre-rock (having developed an allergic reaction to Led Zeppelin in utero?), says McLees, citing the renewed popularity of Tony Bennett. Of Jones’ oeuvre, McLees says, “it’s not boomer, it’s not hippie, it’s not rock, and that’s part of the appeal.” Maybe. But the parents of today’s fans didn’t like Engelbert Humperdinck either, or Tiny Tim, for that matter, and they’re not selling out hot clubs as Jones is. “Also, he’s immensely talented,” says McLees, clinching his argument.

*

Finally, I go to the source, the man his fellow Welsh refer to simply as Jones the Voice. Are you surprised at your popularity with twentysomething fans? I ask.

“No, not really,” says Jones, in a rasp that might indeed induce a more susceptible person to warm up her throwing arm and do something untoward. “I’ve seen it coming. I’ve been wanting it. I’ve been waiting for it.”

Jones says the segue from “Green, Green Grass of Home” to contemporary anthems such as the Wolfgang Press’ “A Girl Like You” was natural for him.

“If I hear a song I like, I want to do it on stage, and nine times out of 10, it’s contemporary,” he says. “Whatever song I do, I’ll inject some soul into it. That’s the way I perform.”

Soul seems an odd quality for a singer from Wales to bring to his work, but Jones explains that he grew up on the blues and other African-American music infused with soul, courtesy of the eclectic programming of BBC radio.

The BBC also introduced Jones to the music of Elvis Presley, later a friend. When the singers met, Jones was thrilled to discover that Elvis had some of his records. (Presley sometimes warmed up before shows by warbling “Delilah.”) “How the hell do you sing like that?” Presley asked him. “You’re partly to blame,” Jones answered.

Although you can hardly explore the depths of a man in a brief chat, it is clear that Jones takes a working man’s pleasure in his success, whatever the age of his fans. His father was a coal miner, and Jones did everything from construction work to selling vacuum cleaners door-to-door. And those were the good jobs, far better than working in a factory. Construction, after all, got him out in the fresh air. And a gratifying number of women who had heard the Voice the night before in a local pub decided this was the perfect day to buy a vacuum cleaner.

However good the day job, show business was better. “It was fantastic,” he recalls. “I was doing exactly what I wanted to do. Being on stage is a blast.”

You sense that if Jones’ new fans suddenly dump him and go running back to Hootie & the Blowfish, he will survive. After all, this is a man who has known one of the highest accolades ‘90s culture can bestow: He has appeared as himself, raising Marge’s estrogen level, in an episode of “The Simpsons.” All Jones needs is a place to stand and material--old or new--that will let him cook. When the sweat begins to run and the crowd begins to roar, Jones is a happy man, with or without flying underwear.

Not that I get it.

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WHERE AND WHEN

Who: Tom Jones.

Location: Universal Amphitheatre, 100 Universal City Plaza.

Hours: 8:15 tonight.

Price: $14.50 to $45.50.

Call: (213) 480-3232.