JESSE The Life and Pilgrimage of Jesse Jackson By Marshall Frady Random House. 552 pp. $28.50

"I AM -- somebody!", people the world over have shouted with Jesse Jackson, making him somebody, indeed. But who is he, really? That so enigmatic a man became heir by default to the Rev. Martin Luther King Jr.'s foundering movement makes it important to know more about him. But it also raises questions about a strain of romantic moralism in our politics that periodically inflames, then depletes, black and liberal movements as well as fundamentalist ones. Marshall Frady has written this hagiography as a romantic moralist: "Absent the great moral dramaturgy of King's day," he writes, "Jackson was left to struggle in the vague spiritual flats of a more prosaic and middling season to find his apotheosis, his mountaintop." On every page, you can feel both subject and author yearning for that mountaintop.

Frady grew up near Jackson's native Greenville, S.C., and attended the white Furman College near Jackson's house in the late 1950s. He didn't meet Jackson until the late 1960s, as a Newsweek reporter, and only later still did he learn that Jackson had watched Furman football games from a black seating area that Frady and classmates had called the "crow's section." Not surprisingly, this Baptist minister's son and biographer of George Wallace brings to Jackson's story a Southern liberal's peculiar moral urgency and strained intimacy; he appreciates much but perhaps atones for too much. At times, the book seems as much Frady's pilgrimage as Jackson's, muddling our reckoning with the man and his "Rainbow."

In powerful chapters on Jackson's early life, Frady shows that his birth to a teenaged mother, after "a feverish liaison with a married man in his mid-thirties," took place in a black community that was otherwise still so deeply churched that its strong moral censure was inseparable from the strong social bonds that help a village to raise a child. With Jackson's shame ("You ain't nothin' but a nobody," children taunted) came a hunger to prove himself to watchful teachers and preachers who gave his talents the moral traction of a clear path toward redemption, a path from which he strays but to which, in Frady's view, he always returns.

It is too easy for Jackson's critics to condemn his foibles and discount his invocations of soul power to free hostages; to "preach the riot out of a crowd" bent on destruction, as he did during the collapse of Resurrection City in 1968 and, 20 years later, to angry blacks ready to invade the Democrats' Atlanta convention; to preach self-discipline and "conservative" social values compellingly to youths even more lost than he was; and to unite white and black voters as none of the other insurgent presidential candidates since Robert Kennedy has done, setting black electoral precedents that, ironically, strengthened Colin Powell's presidential plausibility.

But it's also too easy to swoon over Frady's misty-eyed, mediagenic accounts of Jackson as pilgrim and prophet. Wives of struggling white farmers weep in his arms. Armenian earthquake survivors embrace the man CNN has made a herald of their freedom (and of America's moral greatness). Tribal "kings," tin-pot dictators and Soviet apparatchiks squirm, sometimes melt, at his importunings. But they all become props on Jackson's noisy stage, and Frady's accounts of such encounters implausibly give Jackson the last word before the scenery changes. He omits too many occasions -- like the slaying of a black teenager by a white cop in New Jersey and a California Board of Regents' meeting on affirmative action -- when Jackson dropped in and held forth without knowing what he was talking about.

It's telling that Frady omits Harold Washington's strenuous effort, while grinning through gritted teeth on the night of his victory as mayor of Chicago, to keep Jackson from lifting both their arms high, like a boxing promoter heralding "his" fighter. Gary Rivlin's nuanced Fire on the Prairie describes this and others of Jackson's failures to sustain movement-building "on the ground" in Chicago, including his bunglings of the Breadbasket, Black Expo, and PUSH programs; Frady dashes through all this but dotes on symbolic trips like one to Angola that reappears several times in the book.

Frady does argue that Jackson's strong showings in the 1984 and 1988 presidential primaries "startled all the given political wisdoms" with "an assertive black political force that could no longer be presumed to be a Democratic property free of any real expense." But he doesn't reckon fully with the reality that Bill Clinton became the first Democrat to win the presidency, with overwhelming black support, after repudiating Jackson and his vague agendas. His claim that "Jackson undertook to fashion ... a true, omnibus, populist mass coalition" misses or fudges the difference between televised rallies and real movement-building, between winning primaries and assembling a governing majority or plurality in a general election.

Does Frady ever show Jackson sinning? Sure, as John Bunyan shows Christian in The Pilgrim's Progress, that Ur-text of moral heroes eager to recount their seductions by Mr. Worldly-Wiseman and Vanity Fair. Jackson's egotism, obdurate resentments and financial finaglings appear amid ritual sighing and "spin doctoring" by Richard Hatcher, Herbert Daughtry, Andrew Young, Roger Wilkins, Robert Borosage, and Jackson's wife, Jackie, whose folksy, stagey apologetics Frady swallows whole. He even concludes the famous story of how Jackson smeared his shirt with King's blood and claimed he'd held the dying martyr, by observing that "at least the symbolism of Jackson's story -- a transfer of the commission, signified by a kind of anointing with King's very blood -- would turn out to be largely the reality."

What is reality? In a politics of moral posturing, getting real is less important than being heard: "If you're a human being and weren't affected by what you just heard, you may be beyond redemption," Frady reports Florida Gov. Bob Graham saying after Jackson's magnificent address at the 1984 Democratic convention, which "some commentators" thought "the greatest oration delivered at a presidential nominating convention since William Jennings Bryan's in 1896." But, as Mario Cuomo's eloquence at the same 1984 convention might have taught us, oratory isn't action; a pilgrimage isn't a politics.

A new progressive politics should grasp an irony Frady softpedals: Jackson's big vote in some heavily white areas shows a country less racist than it has been; he has gotten a lot of mileage out of whites' own guilt and goodwill, with this book a case in point. Racism remains, but Jackson's ascent was thwarted less by color than by more intimate hurts and flaws; Harold Washington, Colin Powell and other leaders were born black and poor, too, but not hungry. Their moral journey is the one Jackson's own teachers and preachers envisioned for him, and the one Frady's romanticism obscures. Jim Sleeper, author of "The Closest of Strangers: Liberalism and the Politics of Race in New York," is writing a new book about race.