Kelly Clarkson and the Bubble Gum Machine

It’s a perfect American Idol moment. At the Kodak Theatre in West Hollywood, 48 hours before Jordin Sparks will be crowned winner of the 2007 competition, the champions from seasons one through five, absent Fantasia, have gathered onstage to rehearse a medley of songs from the Beatles’ 1967 LP, Sgt. Pepper’s Lonely Hearts Club Band. Sgt. Pepper is, of course, the landmark album widely considered the greatest long-player in the history of rock & roll, hailed for dragging rock out of adolescent backseats and bedrooms and conferring upon it the intellectual aspirations and emotional complexities of proper art. American Idol, of course, is the phenomenally successful televised singing contest that made Sanjaya Malakar our Beatles.

This year marks the 40th anniversary of Sgt. Pepper’s release, and to the delight of the producers of American Idol, the notoriously protective Beatles camp has granted the show permission to perform four songs from the album. And so, on Wednesday night’s season finale, 30.7 million viewers will be reminded of the sophisticated splendor of the Beatles’ cultural touchstone, and, more subtly but no less pertinent, the peerless clout of the American Idol franchise. Baby boomers, their children and their grandchildren will find common ground, raise their voices as one, maybe sniff back a tear or two, then share a Coke Zero and test-drive a Ford Focus.

There’s only one problem. Well, actually, three. To start, season-two winner Ruben “The Velvet Teddy Bear” Studdard is clearly unfamiliar with the song he’s been asked to perform, “Lucy in the Sky With Diamonds.” It’s quite possible he’s unfamiliar with the group who sang it, too, but never mind. As he squints at the teleprompter, scrolling through lysergic rhymes about “tangerine trees” and “marmalade skies,” Studdard looks vaguely dyspeptic, like an American tourist confronted with a plate of snails.

Carrie Underwood, too, is struggling. Casually beautiful in a black CASH hoodie and cargo shorts, the season-four title holder has drawn the night’s most difficult assignment, “She’s Leaving Home,” one of Sgt. Pepper’s lesser-known tracks. She suffers one blonde moment after another, flubbing lines and missing cues. Her vocals are much like Underwood herself — pretty and slender. Idol producer Nigel Lythgoe, an Englishman who was 18 when Sgt. Pepper came out, appears crestfallen.

To his credit, season-five victor Taylor Hicks knows all the words to “A Day in the Life,” which is good news for Lythgoe and his patient crew, but bad news for the millions who will watch him massacre the song on Wednesday. When Hicks, in full middle-manager-at-karaoke-night mode, mimes holding a gun to his temple as he sings, “he blew his mind out in a car,” you can’t help but wish his finger were loaded.

Then there’s Kelly Clarkson. The inaugural Idol valedictorian and still its most famous alum, the 25-year-old is kicking off the medley with the album’s title track. Dressed in black Lucky Brand jeans, silver Chuck Taylors and a nondescript black V-neck tee, and of ordinary size and build, Clarkson looks less like a pop star than anyone else onstage — or off. Standing alongside guest guitarist Joe Perry of Aerosmith, who even for this run-through is draped in flowing white scarves, she could be the girl from craft services bringing Mr. Perry his tea, rather than a 15-million-selling singer who’s about to release the year’s most polarizing album.

“I want to do this song kinda bluesy, you know?” she’d said earlier. “Like the Hendrix version,” referring to the guitarist’s snarling live take on “Sgt. Pepper.” It’s an obscure, muso reference (truth be told, Blender had to Google it), and not what you’d expect from the onetime costar of From Justin to Kelly. But when the house band and the Aerosmith guitarist strike up the song’s famous opening salvo, and Clarkson nonchalantly bounces her hand off her thigh and begins singing “It was 20 years ago today,” any confusion about her stature vanishes.

The Texas native has one of the great voices in pop music, a powerful and versatile instrument that’s steeped in the rhythm &#amp; blues and country music she grew up with in the South. If Mariah Carey’s five-octave voice is the equivalent of an expensively bred poodle, then Clarkson’s is a bloodhound: friendly, earthy, but fierce just the same. She blasts out “Sgt. Pepper” with startling confidence, unfazed by the song choice, the guitar god to her left, her fellow champs waiting their turn or the dozen 2007 Idol finalists watching, slack-jawed, from their seats. After she nails a goose-pimply gospel run in the chorus, she mock-introduces Taylor Hicks and the stage manager signals cut. The hundred or so showbizzers in attendance — the house band, Fox execs, gaffers, entourages, Sanjaya’s hot sister — spontaneously roar and whistle their approval. Clarkson smiles sweetly, finds her mark and runs through it once again. This time, everyone whoops even louder.

After 90 minutes of hearing the Beatles alternately honored and defaced, Nigel Lythgoe figures that the tribute is about as good as it’s ever going to get, and sends the Idol grads home for the evening. Clarkson is far too polite and low-maintenance to have caused any fuss while the rehearsals dragged on, but she has little time to waste these days. Her new album, My December, written nearly exclusively by Clarkson to the consternation of her record company, has finally been granted a release date, after a hostile and unusually public battle between her celebrated record company boss, Clive Davis, and her high-profile manager, Jeff Kwatinetz — and several months of prerelease promotion are being squeezed into one. Clarkson, though, is a confirmed chatterbox — “I moved so many times growing up, I got good at talking to anyone” — and before leaving, she stops to gab with Underwood (“She looks like Miss Oklahoma,” Kelly says without rancor). Hugs exchanged, she finally heads down to the dressing-room area. Five years ago, in this same concert hall, Clarkson sang the dickens out of the heroically sappy “A Moment Like This” and began her ascent from Burleson, Texas, cocktail waitress to Grammy winner. “When I was onstage just now, all these feelings were coming back,” she says. “I remembered being onstage that night and saying to myself, ‘I don’t want to put out a CD right away, I want to make sure I love everything I do, I don’t want to sell out. Now that people voted for me, I’m going to have this opportunity.’ I kept thinking to myself, Just don’t blow it.”