Washington - With only 18 days left before presidential elections, the US Supreme Court Friday ruled against a voter registration request by Ohio Republicans that could have limited participation by newly registered, mostly Democratic, voters.

The challenge mounted in Ohio was among nationwide protests being filed by Republicans in key battleground states where Democratic nominee Barack Obama has put Republican John McCain on the defensive on normally Republican turf.

The Obama campaign has brought in tens of thousands of new registered voters.

The Supreme Court justices issued an order that blocked a lower court order that required Ohio's Secretary of State Jennifer Brunner to set up a special database of newly registered voters whose driver's license numbers or Social Security numbers don't match records in other databases.

Ohio Republicans said the new database was needed because the state system to verify voter registration information was too cumbersome for local election officials to use.

The Supreme Court issued a two-page order blocking the lower court decision and questioning whether Congress had authorized private litigants to sue under the Help America Vote Act (HAVA.)

The McCain campaign denounced the decision, saying it did not address violations of HAVA and charging that Brunner was acting in a "partisan" manner.

"It remains our belief that American citizens should be guaranteed that their legitimate votes are not wiped away by illegally cast ballots," campaign manager Rick Davis said in a statement.

Brunner had asked the Supreme Court to overrule the lower court order, saying it would create havoc on November 4 election day and allow many voters to only cast irregular ballots, which could then be challenged later by election boards.

Brunner also questioned why the Republican Party had waited until the last minute to challenge the system, when they had two years to do so.

At stake are an estimated 200,000 of the 666,000 voters who have registered since January and show some discrepancies in databases.

Although Obama currently leads by a polling margin of more than 7 per cent, McCain got high marks for his debate performance Wednesday night. A last minute push in large battleground states that are normally Republican strongholds but are leaning to Obama, such as Virginia, Ohio and Florida, could help put McCain in the White House.

Without Ohio's 20 electoral votes, McCain would have to carry every other state that voted for George W Bush in 2004, plus one that voted Democratic, according to Bloomberg's calculation. (dpa)