1965: at last, freedom to vote: forty years ago, police attacks on civil rights protesters in Alabama led to passage of the Voting Rights Act.

Using tear gas, nightsticks, and whips, Alabama state troopers tore into a crowd of hundreds of black marchers crossing the Edmund Pettus Bridge in Selma, Ala., on March 7, 1965. The marchers were seeking the right to vote.

The clash, which came to be known as Bloody Sunday, galvanized the nation. Five months later--and 40 years ago this August--President Lyndon B. Johnson signed the Voting Rights Act into law. In some ways, it was the most important civil rights legislation ever.

Roy Reed, a New York Times reporter, watched the brutal events in Selma from 100 yards away, detained by four troopers, until he could no longer see through a cloud of tear gas.

'WE SHALL OVERCOME'

"Before the cloud finally hid it all, there were several seconds of unobstructed view," Reed wrote. "Fifteen or 20 nightsticks could be seen through the gas, flailing at the heads of the marchers."

Civil rights activists had decided to lead a march that day from Selma to Montgomery to call attention to the plight of blacks in Alabama. In Selma, white officials, including the sheriff, were preventing most of its black residents from registering to vote. A few months earlier, the Rev. Martin Luther King Jr. had exhorted from the pulpit of a Selma church: "We are not on our knees begging for the ballot, we are demanding the ballot."

Governor George Wallace had called in state troopers and they set upon the marchers after ordering them to disperse. Dozens were injured, some severely, including John Lewis, the chairman of the Student Nonviolent Coordinating Committee, a civil rights organization founded by college students in the South. A trooper fractured Lewis's skull. (Today, Lewis is a Congressman from Georgia.)

The events in Selma sparked outrage. President Johnson went on TV to say that all Americans should adopt the cause of Selma's blacks. "It's all of us who must overcome the crippling legacy of bigotry and injustice," he said. "And we shall overcome."

That sentiment had been widely shared among Northern liberals and the Johnson administration. But it was the horror that day in Selma that prompted Congress to act.

The year before, Congress had passed the Civil Rights Act of 1964, landmark legislation that outlawed race discrimination in housing and employment. But it had not addressed the most fundamental democratic right--the right to vote.

Of course, black people--or at least black men--had theoretically had the right to vote since shortly after the Civil War. The 15th Amendment, enacted in 1870, said so. (Women did not gain the right to vote until 1920.)

In the decades after the Civil War, blacks voted and were elected to office in the South. But that stopped around the turn of the 20th century, when white Southerners began efforts to disenfranchise blacks. (The last blacks were elected to the legislatures of Virginia, Mississippi, and South Carolina in 1891, 1895, and 1902. No blacks were elected to Congress from the South from 1901 to 1972.)

GRANDFATHER CLAUSES

White officials used all kinds of devices to keep blacks from voting, including literacy tests, poll taxes, grandfather clauses (requiring proof that one's father and grandfather had been eligible to vote), intimidation, and outright violence.

By 1945, only about 3 percent of the 5 million blacks of voting age in the South were registered to vote.

In Selma, the voter registration office was open only two days a month, and officials moved at a snail's pace, registering about 150 black voters a year. Of the 15,000 eligible black voters in the surrounding county, 335 were registered to vote. (Of the 14,440 eligible whites, 9,543 were registered.)

The Voting Rights Act effectively ended the use of literacy tests and poll taxes, allowed federal officials to register voters, and required some Southern states to get permission from a federal court or the Attorney General before changing voting practices. Forty years later, black voter-registration rates approach those of whites in many areas.

Another result of the Voting Rights Act was the creation of congressional districts made up almost entirely of blacks or Hispanics. Some of these "majority-minority" districts were created to comply with the part of the Act that says states cannot systematically "dilute" minority voting power.

Today, 42 African-Americans sit in the House of Representatives. And this year Barack Obama, from Illinois, became only the third black U.S. Senator since Reconstruction.

SNAKES & INKBLOTS

But critics have objected to oddly shaped majority-minority districts that ended up resembling snakes or inkblots as states attempted to group together blocs of minority voters.

In a 1994 Supreme Court opinion, Clarence Thomas, a conservative Justice who is black, said that districts drawn to ensure black voting power were inappropriate. The government, he said, was involved in "an enterprise of segregating the races into political homelands that amounts to, in truth, nothing less than a system of 'political apartheid.'"

The Supreme Court has since struck down oddly shaped districts in Georgia, North Carolina, and Texas, saying the states could not constitutionally use race as the "predominant factor" in fashioning voting districts. But the decision left states some room to continue creating districts with large majorities of minority voters.

The Voting Rights Act is scheduled to expire in 2007. Some observers say that gains in black voter registration rates and the success of politicians like Obama, who won with both white and black votes, means it's time to scrap the law.

STILL USEFUL?

Others say that would be premature. Anita Earls, a former Deputy Assistant Attorney General in the U.S. Justice Department, wrote in 2003 that the Act was the basis of legal challenges in Florida in the 2000 election, when thousands of voters were erroneously removed from voting lists, many of them black.

"To suggest that the statute has outlived its usefuleness," Earls wrote, "is to misunderstand its purpose and function in our democracy."

TEACHING OBJECTIVES

To help students understand the roots of the 1965 Voting Rights Act, which outlawed race as a bar to voting; and the ongoing debate over some of the effects of that law, including whether it is proper to create oddly shaped voting districts in which blacks or Hispanic voters make up the majority.

LITERACY/ROLE-PLAY: Note that blacks seeking to vote in the South were often required to pass literacy tests. Explain that these tests didn't measure one's ability to read or write, but rather required blacks to define or explain a passage from the Constitution.

You might simulate a "literacy test" by asking a student to read Article I, Section 2, Paragraph 1 of the Constitution aloud. Can students explain what the "Qualifications requisite for Electors" means? Tell them that hurdles similar to this faced Southern blacks who tried to vote.

CRITICAL THINKING: Ask students to discuss majority-minority election districts. First, have a student write these population percentages from the 2000 U.S. Census on the board: white 75 %; black 12.3 %; Hispanic (may be black or white) 12.5%; Asian 3.6%.

Remind students that concentrations of majority and minority populations vary from place to place. Then ask: Is minority voting power "diluted" by mixing a white majority with a black minority in the same district?

Next, have a student draw their state's shape on the board, with an inkblotor snake-shaped election district within that state outline.

Which is more important: That people who live near one another be in the same district? Or that there are enough minority group members in the district so they can elect whomever they wish?

DISCUSSION QUESTIONS

* Should the Voting Rights Act be allowed to expire in 2007?

* Whites who opposed black voting said the policy was a matter of states' rights. How would you answer?

FAST FACT: In January, 79-year-old Edgar Ray Killen was indicted for the 1964 murders of civil rights workers James Chaney, Andrew Goodman, and Michael Schwerner, who were aiding in black voter registration in Mississippi.

Adam Liptak is national legal correspondent for The New York Times.