Washington, DC — A divided Supreme Court on Tuesday struck down a centerpiece of the 1965 Voting Rights Act in a marked victory for Southern states and conservatives that also poses a steep challenge for Congress.

In one of the term’s most highly anticipated rulings, the court ruled 5-4 that part of the 1965 law must be updated to account for how times have changed since Congress first wrote the groundbreaking voting rights legislation.

The ruling could free nine states, as well as certain political jurisdictions in other states, from the necessity of getting prior Justice Department approval for changes that might have an impact on local elections.

“There is no denying that the conditions that originally justified these measures no longer characterize voting in the covered jurisdictions,” Chief Justice John Roberts Jr. wrote for the conservative majority.

The decision in the case brought by Shelby County, Ala., technically leaves in place the so-called preclearance requirements under the law. They require prior Justice Department approval, under Section 5, of everything from buying new voting machines and closing polling places to requiring photo identification and shifting district boundaries.

Practically speaking, though, the decision also effectively pulls the plug on preclearance for the time being, by striking down a related section that sets the formula for determining which political jurisdictions must meet the preclearance requirements. The justices said this part of the law, known as Section 4, was unconstitutional.

“Coverage today is based on decades-old data and eradicated practices,” Roberts wrote, noting that “voter registration and turnout data in the covered states have risen dramatically in the years since.”

In 1965, for instance, only 27 percent of African-American adults in Georgia were registered to vote, compared with 62 percent of white adults. By 2004, African-American voter registration in Georgia had jumped to 64 percent, exceeding white registration. Other Southern states have shown similar trends.

The court’s decision leaves up to Congress the job of updating the preclearance formula, a tough political task that some lawmakers concede may be impossible. Until the formula is updated, however, preclearance itself is up in the air,

Almost immediately after the decision, Texas Attorney General Greg Abbott declared that his state would put into place a controversial voter-identification law without Justice Department approval.

“Well, good luck,” Republican Sen. Orrin Hatch of Utah said of the prospects of Congress passing a new formula. “I don’t think the current Congress has much of a chance to decide it one way or the other because of conflicts in the Congress. That’s a very touchy, very difficult, very sensitive area that’s very difficult to handle.”

Democratic Delegate Eleanor Holmes Norton of Washington, D.C., the capital’s nonvoting representative in the House of Representatives, said Tuesday that she didn’t expect Congress to make any changes this year. At the same time, Norton noted that the last rewrite of the Voting Rights Act, which passed with overwhelming support, had backing from Republican leaders.

“Can they say, ‘Although we stood here in 2006, we’re not going to try to update the formula?’ ” Norton asked rhetorically. “I don’t think they can say that with any credibility.”

In the meantime, Attorney General Eric Holder said Tuesday that the Justice Department “will continue to carefully monitor” political jurisdictions for voting rights impediments and “will not hesitate to take swift enforcement action” when necessary.

Voting Rights Act advocates say that requiring prior Justice Department approval for electoral changes is more effective than chasing after individual violations after the fact.

Nine states currently are covered in their entirety by the preclearance requirements: Alabama, Alaska, Arizona, Georgia, Louisiana, Mississippi, South Carolina, Texas and Virginia. Selected jurisdictions in an additional seven states – California, Florida, Michigan, New Hampshire, New York, North Carolina and South Dakota – also are covered.

The court’s majority reasoned that the different treatment “sharply departs” from the principle that all the states are treated equally.

“While one state waits months or years and expends funds to implement a validly enacted law, its neighbor can typically put the same law into effect immediately,” Roberts wrote.

The court’s other conservative justices – Antonin Scalia, Clarence Thomas and Samuel Alito – joined the decision, as did frequent swing vote Anthony Kennedy.

Underscoring the unhappiness of the more liberal dissenting Justices Stephen Breyer, Sonia Sotomayor and Elena Kagan, Justice Ruth Bader Ginsburg read the dissent from the bench.

“Voting discrimination still exists, no one doubts that,” Ginsburg said, “but the court today terminates the remedy that proved to be best suited to block that discrimination.”

The law, though revised several times, still pegs preclearance coverage in part to voting turnout or registration in the 1964, 1968 and 1972 elections.

When Congress first passed the law in 1965, the preclearance measures were expected to last only five years. Instead, they’ve been renewed with ever-longer extensions. The most recent renewal of the Voting Rights Act, in 2006, extended the provisions for another 25 years. It’s unclear exactly what happens with the preclearance requirements in the absence of a coverage formula.

“I don’t think that we would be able to come up with a remedy that would satisfy this court,” said Democratic Rep. Mel Watt of North Carolina, a key author of the 2006 renewal.

Still, Democratic Sen. Mark Begich of Alaska predicted that lawmakers will make an “aggressive move” to update the formula.

“Because of the ruling of the court, I think there are members who are highly motivated now to bring something forward so we can start discussing in July,” Begich said.

Each year, states and localities submit 4,000 to 6,000 preclearance requests to the Justice Department. Shelby County, in central Alabama, previously has submitted more than 60 such requests.

The case pitted states against one another. South Carolina and Georgia joined two other states in a brief that supported Shelby County. Texas and Alaska added their own similar briefs. On the other side, North Carolina and Mississippi joined California and New York in urging the court to retain the law, saying in a legal brief that “the substantial benefits of the preclearance process have outweighed its burdens.”

Covered jurisdictions could bail out and avoid the demands of preclearance if they could show there was no voting discrimination in the prior 10 years. One hundred and ninety jurisdictions have bailed out so far.

Shelby County, though, couldn’t bail out because of a 2008 redistricting episode involving the city of Calera. The redistricting eliminated Calera’s only majority-black city council district, and city officials went ahead with the election despite Justice Department objections. Without the option to bail out, Shelby County challenged the underlying law.

CORRECTION: An earlier version of this story misquoted Washington DC delegate Eleanor Holmes Norton. A corrected version quotes her as saying: “I don’t think they can say that with any credibility.” (NOT “without any credibility.”)