WASHINGTON, Oct 30 (Reuters) - The U.S. Supreme Court has reinstated Virginia's decision ahead of the Nov. 5 election to purge from its voter rolls about 1,600 people who state officials concluded were not American citizens, though President Joe Biden's administration and voting rights groups said actual citizens were among those struck.

The justices on Wednesday blocked a judge's Oct. 25 order requiring Virginia to restore the affected people's voting registration. It is illegal for noncitizens to vote in U.S. federal elections. Governor Glenn Youngkin, a Republican, on Aug. 7 announced a new policy for culling from Virginia's official voter registration list people "unable to verify that they are citizens," with daily data sharing among state agencies.

The Supreme Court has a 6-3 conservative majority. Its three liberal justices dissented from Wednesday's action.

Youngkin hailed the court's action on an initiative he described as a "critical fight to protect the fundamental rights of U.S. citizens."

"This is a victory for commonsense and election fairness," Youngkin said.

Voting rights advocates and the Justice Department had challenged Virginia's actions.

"The department brought this suit to ensure that every eligible American citizen can vote in our elections. We disagree with the Supreme Court's order," a department spokesperson said.

U.S. District Judge Patricia Giles had decided that Virginia's "systematic program" of voter list maintenance occurred too close to the election in violation of federal law.

Donald Trump, the Republican presidential candidate facing Democrat Kamala Harris in Tuesday's election, has made his anti-immigrant views a centerpiece of his campaign. He and his allies have made claims, without citing evidence, that large numbers of noncitizens could vote in the election. Studies have shown that voting by noncitizens is very rare.

Harris campaign spokesperson Charles Lutvak said the court's ruling did nothing to change the fact that "every eligible voter has a right to cast their ballot and have their vote counted."

"Our campaign is going to make sure every eligible voter is able to vote," Lutvak said, adding that "voting by noncitizens remains illegal under federal law."

With opinion polls showing Harris ahead of Trump in Virginia, the state is not considered among the closely contested ones that are expected to determine the outcome of the presidential race. But with immigration figuring as a key issue in the campaign, court fights over voter list purges in Virginia and Alabama of suspected noncitizens have drawn attention.

In announcing his policy less than three months before the election, Youngkin said the voter-roll maintenance program would include "scrubbing the lists to remove those that should not be on it, like the deceased, individuals that have moved, and non-citizens that have accidentally or maliciously attempted to register."

Virginia already had an existing mechanism to remove noncitizens from its rolls, but Youngkin's executive order increased the frequency of data sharing between government agencies from monthly to daily, and made clear that the process would continue as the election drew closer.

A 'QUIET PERIOD'

At least 18 U.S. citizens were wrongly scrubbed from the voter rolls since the new policy took effect, according to voting rights groups including the League of Women Voters of Virginia that filed a lawsuit on Oct. 7 in federal court challenging the purge. The Justice Department brought a similar challenge four days later. The cases were consolidated.

The challengers argued, among other things, that Virginia's voter roll purge violated a 1993 federal law called the National Voter Registration Act that contains a so-called "quiet period provision" barring states from the "systematic" - as opposed to individualized - removal of people on voter lists within 90 days of an election.

A systemic approach, they argued, risks mistakenly purging valid voters - including naturalized citizens whose state Department of Motor Vehicles documents are outdated - with too little time to correct errors before Election Day.

Of the roughly 1,600 people removed from Virginia's voter rolls since Aug. 7, about 600 had indicated to the DMV that they were not U.S. citizens, according to Virginia's filing to the Supreme Court. The other 1,000 had presented documents to the DMV showing they were noncitizen residents, and were later identified as noncitizens through a federal database, the state's filing said.

Those who were flagged for removal were first notified and given 14 days to affirm their citizenship before being taken off Virginia's list of registered voters, the state said.

Giles, a Biden appointee, on Oct. 25 preliminarily blocked Virginia from enforcing its policy, and ordered the state to restore to the voter registration of the roughly 1,600 people.

Trump called the judge's ruling "a totally unacceptable travesty" and said the Supreme Court "will hopefully fix it."

The Richmond-based 4th U.S. Circuit Court of Appeals on Oct. 27 refused to revive Virginia's policy, prompting the state's emergency filing to the Supreme Court.

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Reporting by John Kruzel and additional reporting by Sarah Lynch; Editing by Will Dunham