WASHINGTON (AP) — The Supreme Court’s conservative justices voiced deep skepticism Wednesday about a section of a landmark civil rights law that has helped millions of Americans exercise their right to vote.

In a fast-paced, 70-minute argument, the court’s liberals and conservatives engaged in a sometimes tense back and forth over whether there is an ongoing need in 2013 for a key provision of the Voting Rights Act of 1965. The measure requires states with a history of discrimination, mainly in the Deep South, to get approval before making changes in the way elections are held.

Chief Justice John Roberts asked the government’s top Supreme Court lawyer whether the Obama administration thinks Southerners “are more racist than citizens in the North.”

The answer from Solicitor General Donald Verrilli was no.

The question, and others like it from the conservative justices, largely echoed the doubts they first expressed four years ago in a similar case that ended without resolving the constitutionality of the latest renewal of the voting rights law in 2006. They questioned whether there remain appreciable differences between the places covered by the law and those that are not. They also wondered whether there was any end in sight for a provision that intrudes on states’ rights to conduct elections and which was regarded as an emergency response to decades of state-sponsored discrimination in voting, despite the Fifteenth Amendment’s guarantee of the vote for black Americans.

While the justices and lawyers uniformly praised the effectiveness of the advance approval requirement since it took effect in 1965, Justice Anthony Kennedy said the country passed other important laws that also ran their course. “Times change,” he said.

If Kennedy sides with his four more conservative colleagues, there would be a five-justice majority to cut back on the law or get rid of it entirely.

As his administration was defending the voting rights law, President Barack Obama was across the street unveiling a statue of civil rights pioneer Rosa Parks, who in 1955 famously refused to give up her seat on a city bus in Montgomery, Ala., to a white man. The court will have to decide whether the conditions that gave rise to that seminal event are, like the statue, a part of history, or whether they persist in parts of the nation.

The court’s four liberal justices appeared uniformly to be willing to defer to the decision by Congress that more progress needs to be made before freeing states from the special federal monitoring.

Those justices aggressively questioned Bert Rein, the lawyer representing Shelby County, Ala., in its challenge to the law.

Justice Sonia Sotomayor acknowledged some parts of the South had changed, but asserted that recent voting rights lawsuits in Alabama suggested that Shelby County, near Birmingham, has not made sufficient progress.

“Why would we vote in favor of your county whose enforcement record is the epitome of the reasons that cause this law to be passed in the first place?” Sotomayor said.

Justice Elena Kagan chimed in that any formula devised by Congress “would capture Alabama.”

In court papers, Rein argued that “dire local conditions” that once justified strict federal oversight of elections no longer exist.

The Obama administration and civil rights groups acknowledge the progress, but also argue that Congress was justified in maintaining the advance approval, or preclearance, provision when thelaw was last renewed in 2006.

Advance approval has been successful because it requires the governments to demonstrate that their proposed election changes will not discriminate, the law’s advocates say. “It moved the burden from victims to perpetrators,” said Sherrilyn Ifill, the head of the NAACP Legal Defense & Educational Fund.

Just last year, federal judges in Washington refused to sign off on two separate Texas plans to institute a tough photo identification law for voters and redistricting plans for the state’s congressional delegation and Legislature. Also, South Carolina’s plan to put in place its own voter ID law was delayed beyond the 2012 election and then allowed to take effect only after the state carved out an exception for some people who lack photo identification.

Opponents say those examples should not be enough to save the measure. Advance approval is strong medicine that has been upheld in the past as an emergency response to longstanding discrimination, lawyer Bert Rein said in his brief for Shelby County.

Congress overstepped its authority when it renewed the law and its formula that relied on 40-year-old data, without taking account of dramatic increases in the voter registration and participation by minorities, or of problems in places not covered by the law, Rein said.

The advance approval was adopted in the Voting Rights Act in 1965 to give federal officials a way to get ahead of persistent efforts to keep blacks from voting.

The provision was a huge success, and Congress periodically has renewed it over the years. The most recent time was in 2006, when a Republican-led Congress overwhelmingly approved and President George W. Bush signed a 25-year extension.

The requirement currently applies to the states of Alabama, Alaska, Arizona, Georgia, Louisiana, Mississippi, South Carolina, Texas and Virginia. It also covers certain counties in California, Florida, New York, North Carolina and South Dakota, and some local jurisdictions in Michigan and New Hampshire. Coverage has been triggered by past discrimination not only against blacks, but also against American Indians, Asian-Americans, Alaskan Natives and Hispanics.

Among the covered states, Alabama, Alaska, Arizona, Georgia, South Carolina, South Dakota and Texas are siding with Shelby County, while California, Mississippi, New York and North Carolina argue that the law should be upheld.

Nearly 250 of the 12,000 state, county and local governments covered by the law have used an escape hatch to get out from under the special oversight by demonstrating that they and smaller places within their borders no longer discriminate in voting.

Thousands more jurisdictions also may be eligible, said voting rights expert Gerry Hebert. But that list probably does not include Shelby County, because one of its cities, Calera, defied thevoting rights law in 2008 and provoked intervention by the Justice Department in the Bush administration.

A decision is expected by late June.

The case is Shelby County, Ala., v. Holder, 12-96.