Baring the Celtic Soul of U2 : UNFORGETTABLE FIRE Past, Present and Future, the Definitive Biography of U2 <i> by Eamon Dunphy (Warner Books: $16.95; 320 pp.)</i>

Eamon Dunphy’s U2 biography is the only rock book I know whose index includes a listing for Lourdes. The reference is to the fact that their manager, Paul McGuinness, worked there briefly as a tour guide, but given this band, it wouldn’t surprise you had Dunphy claimed a more direct connection. U2’s combination of social concern and passionate spirituality has made the Dublin quartet a uniquely powerful voice in rock today: Audiences respond to them as charismatic, in the old-fashioned as well as the contemporary sense.

The band’s breakthrough album, this year’s Grammy winner, “The Joshua Tree,” exalted lead singer Paul “Bono” Hewson’s search for meaning to unprecedentedly evangelical heights. Most fans and critics greeted it with rapture--however much, for those of us who have stayed dubious, the record’s lofty tone suggested that the mantle was one U2 had grown more than willing to accept. They aren’t famous for their irony.

Dunphy shares the beatified view of U2’s importance, but from his own angle. An Irish journalist--and one, judging from his commentary, not otherwise much interested in music--what matters to him is U2 as vindications of the old sod. His tetchy national pride is barely concealed; the best instance of it comes early on, after a description of the dingy neighborhood Hewson’s father, Bobby, called home. “But because this was Dublin,” Dunphy bristles, “the area possessed a vitality absent from lower-middle-class existence elsewhere.”

Some may find such parochialism grating. But to me it’s the book’s value--a good corrective to the universalist aura attributed to acts such as U2 over here, which mostly only reflects the North American audience’s complacency.

It’s hard to imagine a comparable account of a U.S. band that put so much emphasis on the political situation the members grew up in, and treated their family and religious backgrounds, and which schools they went to, in such polarized terms. In Dublin, those are traits, not circumstances, and trying to escape them only leads to new conflicts: Hewson and the band’s other creative force, guitarist “The Edge” (Dave Evans in civil life), took refuge from Ireland’s schisms in the ecumenical Christian sect they apparently still belong to. They then faced a crisis when Evans was unable to reconcile his faith with his choice of career.

The first third of “Unforgettable Fire” makes a good case for these musicians as products of an environment whose particulars are too easily misunderstood. It helps that Dunphy himself is so embroiled in it all; for all his writing’s florid qualities, he’s at home with issues and complexities that would leave most rock biographers floundering.

The book’s later sections, after the band’s success, take on the proportions of a triumphal march--simple-mindedly so. We never quite learn how The Edge resolved his religious doubts. (Assuming his sincerity, it’s hard to see how he could: Of course this music is self-aggrandizing, above all when it’s pretending otherwise.)

The peculiar nature of U2’s popularity--the way Hewson uses momentous political and social topics to air a purely spiritual anguish, to an effect ultimately quietistic rather than engaged, and the way people who’d snicker at televangelists respond so unreservedly to having their yearnings for faith expressed in the secular, rock ‘n’ roll context--deserves a more considered treatment than it’s given here.

The author’s lack of musical credentials also leaves his picture of his subjects’ place in the rock pantheon rather confused. At some points, he seems to suggest that rock was a basically frivolous proposition until U2 got in on it. Elsewhere, he praises them as a return to “decency”--apparently without grasping that such pieties were what most rock was rebelling against, which is why this band’s case is so paradoxical. One can be roused by their music (although their sound is hardly as lacking in precursors as Dunphy supposes) and still think that the liberation they celebrate is of a highly regressive sort. Unwittingly, Dunphy reminds you that one thing no great rock band has ever been is humorless.

They’re still plainly a substantial if narrow band, with a few songs of undeniable power--particularly “Pride (In The Name of Love),” a tribute to Martin Luther King in which the musical grandeur is for once appropriate. In its seriousness and wealth of biographical detail, “Unforgettable Fire” should please almost any confirmed fan. But, as one of the skeptics, I would have liked to see my reservations better addressed, if not rebutted. Instead, I was left with the uncharitable thought that I prefer my revivalism straight; U2 is probably more in earnest, but Aimee Semple McPherson knew more of the ways of the flesh.