From the sun-dappled park comes the background rhythm of urban life, the slap-slap-slap of basketballs on blacktop. Across the street, in a small convenience store, and in profound peace of mind, sits the proprietor, selling eggs and reading the Koran.

He is Jamil Abdullah Al-Amin. He is 41. He used to be H. Rap Brown. But that was long ago and, in a sense, in another country. It has been a winding and ascending path from his boyhood in Baton Rouge to Atlanta's west end. The hyperkinetic human torch of urban unrest, circa 1967, is, in 1985, enveloped in a strange serenity in a city known for its hum of energy. The man who was the hammer of America, or at least of Cambridge, Md., has become a merchant, but with this distinction: He is, at last, really radical.

That radicalism was a short candle. It was rhetorical radicalism, elicited from young people by older flatterers and amplified by the media 18 years ago. Today, and for the long haul, Jamil is in inner emigration, out of his country and into Islam.

He burst upon the nation in the 1960s, when the socal air was composed of, in the words of a Rex Stout character, "oxygen, nitrogen and odium." He succeeded Stokely Carmichael as head of the Student Nonviolent Coordinating Committee, which soon changed the second word to "National." He said the sorts of things that then passed for trenchancy: "If you give me a gun, I just might shoot Lady Bird." The only lasting legacy of his brief blast of prominence is an aphorism: "Violence is as American as cherry pie."

The 1960s were God's gift to conservatism, a decade dominated -- not numerically, but culturally -- by overreachers. Those years were noisy with the voices of fundamentally frivolous people feigning seriousness; people convinced that sentiment is the meassure of virtue, that rhetoric is the measure of sentiment and that morality is a state of mind: I feel, therefore I am. This radicalism helped produce two significant effects: the "backlash" candidacy of George Wallace and the presidency of Richard Nixon.

"Many people," Jamil says, "reckon time from the '60s. Time stopped for them then. I don't miss the '60s." Now that Brown is someone else, and quite quiet, he is, at last, impressive. He is 6 feet 5 inches tall and gestures slowly as he speaks, pointing with fingers that should belong to a pianist.

There are many Muslims in his neighborhood. The store next door sells incense and Arab-style garments. Many of his customers, including a 3-year-old seeking six eggs, wear the kind of crocheted cap he wears beneath a gray cloth. His shelves are sparsely stocked, but his customers are buying only Cheerios and milk a few dollars worth at a time, and anyway, commerce is not the point. The Koran is the point -- every point.

After inciting riots in Maryland and elsewhere and getting into a shootout with police in New York, he served five years in jail. But by 1971 he had converted and had concluded that the change that matters is the one the changer can control: the soul. Democracy is less a creed than a climate of opinion. His interest is in a creed. He prays five times a day and fasts during Ramadan.

The transmission of religion to the rising generation is never easy, and inoculating Muslim children in the middle of a metropolis against the temptations of American youth culture will be especially difficult. To that end, he and neighbors (he was chosen imam of his community) are founding a religious school.

Kierkegaard said Christianity is not glad tidings to the unserious because it seeks first to make them serious. Religion has done that for Jamil, who shows a flicker of levity only when asked whether he goes to see the undistinguished Atlanta Hawks play basketball: "No, I go to see the other teams play."

Driving a Toyota van on one of the freeways that have made this city a symbol of Dixie transformed, Jamil reaches behind him for a plastic carrying case, removes from it a cassette, slips it into the dashboard tape deck and the van is filled with the almost musical sound of passages from the Koran, recited in Arabic and then in English. This might seem like another example of America's amazing capacity for absorption. But to give Jamil his hard-won due, he has not been absorbed.

Members of Atlanta's large black middle class are driving all around him on the freeway. But H. Rap Brown, a boy from America's South, has become a man of a distant East.