A predictably divided Supreme Court appeared ready to strike down -- at least in part -- the key enforcement provision of the landmark Voting Rights Act of 1965, with many conservative justices on Wednesday suggesting it was a constitutionally unnecessary vestige of the civil rights era.

Known as Section 5, it gives the federal government open-ended oversight of states and localities mostly in the South with a history of voter discrimination.

Any changes in voting laws and procedures in all or parts of 16 covered states must be "pre-cleared" with Washington. That could include something as simple as moving a polling place temporarily across the street.

The provision was reauthorized by Congress in 2006 for another 25 years and officials in Shelby County, Alabama, subsequently filed suit, saying the monitoring was overly burdensome and unwarranted.

In a tense 80 minutes of oral arguments, Justice Sonia Sotomayor asked why the court would rule "in favor of the county that is the epitome" of what caused the law to be passed in the first place.

Her three reliably liberal colleagues appeared to support continued use of the coverage formula run by the federal Justice Department.

But Justice Samuel Alito wondered why some states were subject to oversight and not others.

"Why shouldn't it apply everywhere in the country," he asked. The other four more conservative justices had tough questions for the Obama administration's positions.

This case will be one of the biggest the justices tackle this term, offering a social, political, and legal barometer on the progress of civil rights in the United States and the level of national vigilance still needed to ensure minorities have equal access to the election process.

A ruling in this appeal is expected by June.

Justice Antonin Scalia produced gasps in the courtroom when he reiterated concerns by some observers that reauthorization of the voting rights act by lawmakers seven years ago was due in part for political expediency.

"I think it is attributable, very likely attributable, to a phenomenon that is called perpetuation of racial entitlement. It's been written about. Whenever a society adopts racial entitlements, it is very difficult to get out of them through the normal political processes," he said.

"I don't think there is anything to be gained by any senator to vote against continuation of this act. And I am fairly confident it will be reenacted in perpetuity unless a court can say it does not comport with the Constitution," he said.

Sotomayor later asked the attorney for Shelby County whether he endorsed Scalia's comments.

"Do you think that the right to vote is a racial entitlement in Section 5?" said Sotomayor.

Attorney Bert Rein acknowledged that in 1965, at least, "it was intended to protect those who had been discriminated against."

Civil rights groups say Section 5 has proven an important tool to protect minority voters from local governments that would set unfair, shifting barriers to the polls. If it is ruled unconstitutional, they warn, the very power and effect of the entire Voting Rights Act would crumble.

But opponents of the provision counter it should not be enforced in areas where it can be argued racial discrimination no longer exists.

The appeal presents the court and its shaky conservative majority with two of the most hotly debated issues in politics as well as constitutional law - race and federalism.

It will be a major test of Washington's authority, and the extent to which the federal government may consider vestiges of voting discrimination that may still linger, potentially keeping some minority voters disenfranchised.

The Voting Rights Act was a monumental political achievement during the Civil Rights era. It banned such things as poll taxes and literacy tests that had long suppressed black voter turnout. States like California and Texas also have a history of discrimination against Hispanic voters.

The justices used competing statistics in Wednesday's public session to make their points.

Justice Elena Kagan pointed out Alabama was about a quarter African-American, but has no black statewide elected officials.

"If Congress were to write a formula that looked to the number of successful Section 2 [VRA] suits per million residents, Alabama would be the Number One state on the list," she said.

But Chief Justice John Roberts told the government lawyer: "Do you know which state has the worst ratio of white voter turnout to African-American voter turnout? Massachusetts. Do you know what has the best, where African-American turnout actually exceeds white turnout? Mississippi."