So how do you start pinning down this often angry, always argumentative, absolutely restless, sometimes sprawling and curiously contradictory hybrid of an album that - it should go without saying - is the most ambitious record U2 have yet released?

Could I suggest it concerns George Bush's - no, sorry - his handlers' opinions of Bruce, Springsteen's "Born In The USA" and Jimi Hendrix's Woodstock pledge of allegiance; Jimmy Swaggart and the broadcasting "Towers Of Steel" where -Belief goes on and on"; U2's allergy to Levi's commercials and every record executive guilty of stonewashing spontaneous human imperfection out of the recording process; Heaven and the art of rock'n'roll motor-cycle maintenance; the mouth-to-mouth resuscitation of the ailing body of rock history that even they sometimes nightmarishly fear may revive as Frankenstein with a Fender; their own special American edition of The Crane Bag, Christ at Harlem's Apollo Theatre or The Confessions Of a Cedarwood Road Soul Singer; a desperate attempt to ward off the touring hazards of delinquency, boredom and the redecoration of hotel bedrooms; their own Irish emigrant's letter from America - a post-graduate thesis; a collective two fingers to Albert Goldman; the absolutely vital distinction between a blindman's cane and a sheet-stain; and finally, the moment in which U2 don't so much just trust their instincts as recover, exercise and learn from them - as if they feared those faculties could be emasculated by disuse - by exploring beyond "Bullet The Blue Sky" to fall into (and sometimes recoil from) the arms of America, an embrace that finds them simultaneously blinded, liberated and fixated by the myths they wrestle with?

Among other things. Including the humour behind Adam Clayton's chuckle when film director, Phil Joanou, pretends to be a long-winded interviewer, inquiring about the gestation and birth of this rough beast. Because, since "Rattle And Hum" is one of the kaleidoscopically self- referential album of the tour of the book of the film species (Consumer warning: this review probably will be subject to revision once I see the movie), it's all too easy to stumble down blind alleys or be trapped into false conclusions on first acquaintance. Double-albums are always unwieldy affairs but U2 dare further hazards of misinterpretation by segmenting the live tracks with new material that not only takes up 60% of the running time but also exposes an entirely new re-orientation, breaking up - and making up - the band again but, this time in full and potentially unforgiving public glare.

The first three tracks are the introductions, to ease the listener into "Rattle And Hum"s challenging diversity of moods and styles. "Helter Skelter", never performed live by The Beatles, can be heard as a metaphor for the re-creation of personality on the concert stage but it's also the first clue that among this album's themes will be ecstasy, and its attendant hangovers and tristesse; "Van Diemen's Land", sung by Edge as a sparse folk ballad, sets up a separate theme of travel, displacement and emigration; and "Desire", grounded on a Bo Diddley/Rolling Stones' "Not Fade Away" riff, and smeared by a cheesy organ that could have been sampled from any Tommy James And The Shondells' record, further widens the stylistic terms.

But, after these foothills, " Hawkmoon 269" is the first assault on the summit. With the assistance of timpani and percussion, Larry Mullen's drumming is elementally studio-shaking, as Bono amplifies the themes of love's possession and compulsiveness first aired in "Desire", on a performance where producer, Jimmy Iovine, once a John Lennon collaborator, seems to be urging U2 on, to outsmart and outreach Phil Spector's muffled Plastic Ono Band productions.

For "Rattle And Hum" also concerns idols. Lennon is one whose influence will re-emerge later but a second is Bob Dylan, whose organ underpins "Hawkmoon 269" and whose "All Along The Watchtower" launches side two - a live version from the San Francisco "Save The Yuppie" free concert. "AII I've a got is a red guitar, three chords and the truth," shouts Bono. Overblown rhetoric? We'll also return to that issue later.

By now, it's abundantly clear that this is no longer the U2 U U(sed) 2 know. The band, who once glided and cruised in the fluent jetstream of The Edge's almost orchestral vibrations, now rattle and hum, acting as if they're on a dune buggy or express train, greedily scanning the sights out of the windows, gesturing to each other since they can't talk for the R'n'B radio blaring out at full volume, overloaded with the accumulated static of history.

Retro-romance? That's another issue since the live version of "I Still Haven't Found What I'm Looking For" follows, as the next attack on the peak. Recorded in New York with a gospel choir, the New Voices Of Freedom, this version fearlessly, ferociously and yet upliftingly pumps up the emotional volume inherent in the song's dilemma, a performance that affirms the absolute life-giving necessity of honest inadequacy and doubt, over death by dogma and spiritual pride.

Among other things again. Because, by now, it's also abundantly clear that U2 are struggling to clean not only the windows of any heavenly mansions on the hill but also those of Graceland, whilst only haunted by the suspicion that if they ever truly espied the Pearly Gates, they'd find St Peter and Elvis Presley negotiating a Pepsi sponsorship deal with Jim and Tammi Bakker (who've definitely found what they're looking for).

But not with Martin Luther King, who increasingly becomes this live side's guiding light. U2 don't approach black music with those London clubland values that can both equate community with conspicuous consumption, and tend to screen out both the politics and spirituality in Sixties soul. Indeed, it's almost as if they've unconsciously happened on the Washington civil rights march, and not Woodstock, as the touchstone of stadium rock.

So they drop in 38 seconds of black street singers, Sterling Magee and Adam Gusson's "Freedom For My People", invoke Martin Luther King's name on "Pride(in The Name Of Love)" and unleash the first political punch on "Silver And Gold" with an Afrikaaner-accented diatribe against apartheid from Bono - though I confess that all later versions pale for me after the solo original.

But on side three, the public ego is put aside. "Angel Of Harlem" is a beaut. Almost as if the colours of all traditions do sometimes bleed into one, an Irish band ventures into Sun Studios to collaborate with the Memphis Horns and Cowboy jack Clement on a song for Billie Holliday. And by the final verse, Bono the empathiser and enthusiast is so immersed in her, you almost believe he'd use the whole side if not the complete album to sing her praises - except that he spent all the previous night in a Memphis bar in infatuated talk about the subject and, besides, probably forgot all the paper napkins he's littered with his notes. I'd say there's a second there, sir, 'cept "Angel Of Harlem" is so ace.

Bob Dylan then returns as co-author of "Love Rescue Me". Definitely a song that can get neglected on early hearings, this country-soul ballad - it would have been ideal for William Bell or Percy Sledge - casts a cold, private eye on fame with its key lines, "Many lost who seek to find themselves in me/They ask me to reveal/The very thoughts they would conceal," as Bono wails sufficient to greet the ghost of Otis Redding on the close.

By now Love has become the face of salvation, they emphasise. And when the next guest, B.B. King ducts on "When Love Comes To Town", the traditional scheme gets reverted as the bluesman, the devil's musician, sings the verses of Christian redemption.

But then as "Heartland" closes the album's most impressive side, U2 suddenly double back (or is it forward?), Brian Eno and Daniel Lanois re-emerging as aides. We're still in America, in "Mississippi and the cotton wool heat" but this is a gauzy, heat-dazed, impressionistic track, almost as if they're showing how they'd rewrite "The Unforgettable Fire" in '88.

You also become aware now, listening to "Rattle And Hum" what U2 select from America - the ecstatic, the incantatory, the inarticulate speech of soul-searching American hearts rather than a country 'n' western strain of story-telling realism. These songs switch from public ceremony to private doubt, from the stadium to the studio, generalising experience through the first person, and are usually unpeopled, except when U2 cast themselves in the role of fans, as in the case of "Angel Of Harlem".

Or in the angry, argumentative "God Part II", their tribute to John Lennon which again doubles back as Bono screams "I don't believe in the 60's, in the golden age of pop/you glorify the past when the future dries up."

This, even as they use Jimi Hendrix's "The Star Spangled Banner" to preface "Bullet The Blue Sky". What's more, they seem to confuse the issue even further with the last track, "All I Want Is You" which follows "Heartland" in reference back to "The Unforgettable Fire", thus ending "Rattle And Hum" ‘s excavation of rock's roots with a full minute of Van Dyke Parks' uneasy strings.

Too much confusion... all along their watchtower? No. At the last moment, U2 sway back from the jaws of revivalism. Spirit will always win over style for them and they really should have dedicated this album to Levi's for inspiring them to cut through the crap that has latterly domesticated the history of American music. Ultimately "Rattle And Hum" is their mission to rescue, re-energise and recast lost and dying spirits from those media homes where they'd ultimately be patronised and pensioned off.

Because "Rattle And Hum" is also a defiantly American and populist album. The point of U2 is that they are fired by an unshakable conviction that someone must still fight for that vast, unclaimed territory of popular culture between George Bush and the hardcore, lest nothing be heard beyond the hissing of summer lawns and Whitney Houston albums. But if they double-back, as they regularly do towards the close of "Rattle And Hum", it's to escape the triple demons of pastiche, dogma and any form of renewed rock tribalism.

And yes, of course, "Rattle And Hum" is populist, a stance highly unfashionable among those who fastidiously despair of popular culture, who, in their secret treason see the only useful remaining creative activity as the preserve of those marginalised dandies of the soul, who refine emotions and experiences untranslatable to the public arena.

Meanwhile, I'm left pondering just one of its multifarious conundrums - what's the connection between a blindman's cane and a sheetstain? Now And Zen you might profitably ponder that.