Garth Brooks, the biggest-selling solo artist in the history of American music, is about to pull a disappearing act. However, Brooks being Brooks, this will be the most public disappearing act since Jimmy Hoffa.

On Tuesday, Capitol will release "Garth Brooks in . . . The Life of Chris Gaines." It's not a Garth Brooks album. It's a Chris Gaines album. It's not a country album. It's an accomplished rock and R&B-focused "greatest hits" collection.

Not familiar with Chris Gaines? You will be.

Brooks is about to embark on one of his familiar media blitzes--partly in character. Tomorrow he'll be on "The Tonight Show With Jay Leno," Tuesday on "The Rosie O'Donnell Show" and "Late Night With Conan O'Brien." On Wednesday, after appearances on "Today," "Later Today" and "Showbiz Today," he will star in an hour-long special on NBC. And VH-1 is preparing a "Behind the Music" special as well.

Here's the concept: Chris Gaines is a fictitious pop star, and this album is a career retrospective as well as a "pre-soundtrack" for "The Lamb," a film about Gaines (starring Brooks) that's tentatively slated to come out late next year. The film will then produce a real soundtrack with totally different Gaines songs.

And here's a quick Gaines bio: Born in Australia in 1967 to an Olympic swimming coach and his medal-winning wife, Christian Gene Gaines moves with his family to California at age 5. In 1986, he plays guitar in a one-hit band, Crush, reluctantly moving to a solo career when that group's lead singer dies in a plane crash. Gaines's debut album, "Straight Jacket," sells 16 million copies and wins the Grammy for Album of the Year.

But in 1992, tragedy strikes and after Gaines survives a near-fatal car crash, he undergoes both extensive plastic surgery and serious soul-searching. When he reemerges in 1996 with the "Triangle" album, he's hailed as "The New Prince." Now, with his greatest-hits package heading into stores, Gaines is about to begin recording "The Lamb," which according to the extensive back history provided by Capitol, will be "the definitive album of the new millennium."

All right, admit it: Right now, you're thinking "This Is Spinal Tap" or "The Rutles." But those were genre- and act-specific homage/parodies depicting magnificent failures. The conceit behind ". . . The Life of Chris Gaines" is that it's hit-filled.

The surprising thing is that it could well produce some hits in some very unlikely places.

That's because there's only one country-tinged song--"It Don't Matter to the Sun"--where Gaines sounds anything like Brooks. Instead, the singer spends much of the album singing in a higher register than his familiar baritone, often slipping into convincing falsetto on smooth R&B ballads that could easily fit on urban radio.

And when he leans more to rock, Gaines sounds positively like Bob Dylan on "Main Street" and like Jakob Dylan on the Wallflowery "Unsigned Letter." He also evokes "Eleanor Rigby"-era Beatles on "Maybe."

If all this sounds like precious pastiche, it doesn't end there. The cover of ". . . The Life of Chris Gaines" features a hatless Brooks in a black shirt, sporting dark bangs and pasty/gaunt looks, a wisp of whiskers under the lips--your basic Chris Cornell/Prince look.

All the hype--typical of every new Brooks project--is likely to take attention away from the actual musical accomplishments of ". . . The Life of Chris Gaines." After all, Brooks may be the best-selling artist of all time, but he's hardly one of the most beloved, particularly in recent years when it seemed his major ambition was to surpass the Beatles as best-selling act of all time.

The score: Since 1963, the Beatles have sold 105 million records; since 1989, Brooks has sold 90 million. A new Christmas album in November will undoubtedly push that total higher, but ". . . The Life of Chris Gaines" is likely to be more problematic.

That's because country fans and the crossover pop fans who elevated country music sales in the early '90s may not want to follow Brooks as far as he wants to take them. Rock and R&B fans, traditionally cynical about country music, may resist Brooks as an egotistical interloper. And though radio has been both curious and supportive--pop and R&B stations are playing "Lost in You," country stations "It Don't Matter to the Sun"--they're looking for real hits, not imagined ones.

So, what are the album's prospects?

Surprisingly good, thanks to producer Don Was--a well-known career revival specialist--and strong writing headed by Gordon Kennedy, Wayne Kirkpatrick and Tommy Sims, who previously teamed up on Eric Clapton's Grammy-winning hit "Change the World." Kennedy and Sims, alumni of the contemporary Christian country act Whiteheart, form an excellent core band with Kirkpatrick and drummer Chris McHugh.

Curiously, ". . . The Life of Chris Gaines" is set up counter-chronologically, so that Gaines's first foray into pop as guitarist in the cleverly Beatlish "My Love Tells Me So" (Kennedy handles the lead vocal) closes the album, preceded by some of those early solo hits, the chugging Doobie Brothers-style "White Flag" and a Fleetwood Mac/Toto-style "Digging for Gold" (cynically challenging motivations in a May-December marriage). The best of these is "Maybe," where George Martin-inspired strings and horns, aching George Harrison-ish guitar and wispy Paul McCartney-esque vocals recall "Eleanor Rigby," "Yesterday" and "Blackbird."

The middle portion of the album includes "It Don't Matter to the Sun," a melancholy, piano-driven meditation on heartbreak ("I'm still in love, so why aren't you?") that provides a rare encounter with Brooks's baritone. "Main Street" sounds like the Band backing Bob Dylan on "Knockin' on Heaven's Door" and depicts a familiar small-town drama, where blue-collar frustrations intrude on romantic ideals.

And those tired of waiting for the next Wallflowers album will be thrilled with "Unsigned Letter," a soft-spun modern rock venture built around Hammond B-3 organ, trebly guitar, quietly propulsive rhythms, husky vocals and tortured lyrics. No less catchy is "Way of the Girl," with brittle guitar and power-rock verse juxtaposed with an airy funk chorus.

The highlights of ". . . The Life of Chris Gaines" come from its most surprising stretch: Garth Brooks as soul man. It's not likely anyone would have identified Brooks as the vocalist on "Lost in You," "Driftin' Away" or "That's the Way I Remember It." Better guesses would have been Babyface, Tony Rich, Tracy Chapman, maybe Kenny Loggins. It's not just that Brooks/Gaines is working in a higher register; the emotional timbre is convincing, the fragile falsetto and unfamiliar cadences unforced.

The best of these songs is the ballad "Lost in You," very Babyface-ish in its spare, supple acoustic production and the charming romantic exhilaration of its lyrics: "You are my godsend/ That I have been forever dreaming of/ My angel from above, heaven knows/ I'm head over heels and it shows."

Almost as good is "Driftin' Away" and "That's the Way I Remember It." The first is a stripped-down acoustic plaint in which a repentant lover dissuades a still-hopeful partner, telling her "I'm not quite sure that you can trust me/ I'd hate to have you find me again, baby, like the wind, driftin' away."

As for "That's the Way I Remember It," it's a paean to the good memories that survive faded love, a shimmering shuffle with a yearning vocal full of tremble and tenderness. "Some of our stories fade as we grow older," Gaines muses, "some of them get sweeter every time they're told."

The albums kicks off with what is ostensibly a new Gaines song, "Right Now." It's actually a trendy melding of Cheryl Wheeler's anti-violence, pro-responsibility anthem, "If It Were Up to Me" (its lyrics spoken as disembodied rap) and the soaring inspirational chorus from the Youngbloods' 30-year-old hit "Get Together." The song seems particularly prescient in the wake of the school shootings that have rocked America in the last year.

So, will Garth Brooks fly as Chris Gaines? It would be ironic, of course, should urban radio prove the most receptive format to this radical reinvention. Brooks is clearly having fun--witness the detail of Gaines's back story, including mock album covers and personal tragedies--but as a hard-driving entrepreneur and marketing whiz, he's also taking a huge risk with this project. It would have been interesting to gauge public reaction absent the hype, to see how far the music itself would have carried the album. It might not do much for Garth Brooks, but it just might turn Chris Gaines into a star, after all.

(To hear a free Sound Bite from this album, call Post-Haste at 202-334-9000 and press 8181.)