Fearing "trouble," he decided it would be safer for us to visit the battlefield at Gettysburg. The irony was lost on me for years.

Not until I read Drew Hansen's instructive slice of history, "The Dream: Martin Luther King Jr. and the Speech that Inspired a Nation" (Ecco, $23.95), did I realize that my father was among many who feared the March on Washington.

As Hansen recounts, the Justice Department was prepared to declare martial law in the event of a riot. The Army told the FBI that it had 17,000 combat-ready troops nearby. On the eve of the march, alcohol sales were banned in Washington, prompting Malcolm X to joke, "No firewater for the Indians tomorrow."

Members of Congress told their female employees to stay home and lock the doors because the streets wouldn't be safe. The Catholic archbishop ordered nuns to stay inside.

But on Aug. 28, 1963, some 250,000 people peacefully marched to the Lincoln Memorial where King, the final speaker, delivered his 17-minute "I Have a Dream" speech, one of the most famous in American history.

Hansen, 30, a lawyer in Seattle, wasn't even alive then. But as a student at Yale Law School he studied civil rights, and as a Rhodes Scholar at Oxford he studied theology — a perfect background to offer a new perspective on what King said that day, how he said it and what it has come to mean.

Hansen places the march in context, noting that in 1963 many Southern states operated segregated schools in open defiance of the Supreme Court. He writes, "Not a single black child in South Carolina, Alabama or Mississippi attended an integrated public school during the 1962-63 school year."

Similarly, many Southern counties barred blacks from voting. Panola County, Miss., had 7,250 blacks of voting age. The only black voter was 92 and had registered in 1892, during Reconstruction.

Hansen traces King's rapid rise within the civil rights movement, but notes he was given the final speaking slot in part because other speakers thought the TV crews would be gone by then to process their film for the evening news.

The heart of the book is the speech itself: how King followed his prepared remarks, about the need for civil rights, for 10 minutes, then improvised the rest, a vision of an end to racism, the part that's remembered and recited.

Hansen devotes 15 pages to a side-by-side comparison between the speech King prepared and the one he delivered. He concludes, "Had King not decided to leave his written text, it is doubtful that his speech at the march would be remembered at all."

For the first time, a national audience saw a "pulpit performance that those active in the civil rights movement could see several times a year," Hansen writes. "King transformed a political rally ... into a vast congregation." He prepared a formal address, "but ending up preaching a sermon."