Dec 2 (Reuters) - Senate majority leader Harry Reid has scheduled a cloture vote next week on the nomination of Caitlin Halligan to the District of Columbia Circuit Court of Appeals, setting up a likely showdown on the controversial nominee.

On Thursday night, Reid scheduled the vote, which would formally end debate on Halligan's nomination, for Tuesday, Dec. 6. The Obama administration needs sixty votes for cloture, a difficult hurdle because it would require seven Republicans to cross party lines.

Earlier this year, the nomination of Goodwin Liu to the 9th Circuit Court of Appeals, was effectively blocked after Democrats couldn't achieve cloture. Liu was later confirmed as a justice on the California Supreme Court.

Legal observers see Halligan as a key nominee for President Obama, who has struggled to get federal judicial nominees appointed. In George W. Bush's first term, the Senate confirmed about 200 of his nominees. Obama has had about 120 nominees confirmed so far, and the confirmation rate is likely to slow over the next year in the run-up to the election.

Nominations to the D.C. Circuit are often subject to higher scrutiny because the court, which handles major political, regulatory and financial cases, has traditionally been a breeding ground for Supreme Court Justices. Four of the Court's current members -- Chief Justice John Roberts Jr. and Justices Antonin Scalia, Clarence Thomas, and Ruth Bader Ginsburg -- came from the D.C. Circuit.

"I expect a fairly close vote," said Carl Tobias, a professor at the University of Richmond School of Law. "It's the potential for any D.C. Circuit nominee to go the Supreme Court -- that's why they get the most scrutiny."

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Halligan, who is currently general counsel for the New York District Attorney's office, was nominated by Obama in September 2010. She previously served as New York state's solicitor general, a partner at Weil, Gotshal & Manges, and a clerk to Supreme Court Justice Stephen G. Breyer.

Halligan has been supported by liberal-leaning groups such as the National Women's Law Center, which is advocating for more women on the bench, and opposed by conservative-leaning groups such as the National Rifle Association, which cited her representation of New York State in litigation against gun manufacturers.

The Republican National Lawyers Association has also come out against her nomination, claiming that she made inconsistent statements about her judicial philosophy. In Senate testimony, the association says, Halligan wasn't candid about her views on the Constitution as a "living document."

In an indication of the difficulty Halligan's nomination is likely to face, the Senate Judiciary Committee -- which unanimously approves an overwhelming majority of judicial nominees -- only narrowly approved her nomination last March by a 10-8 vote.

(Reporting by Carlyn Kolker)

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