WASHINGTON - Senate Republicans on Tuesday blocked President Obama's nominee to the U.S. Court of Appeals in Washington, partly as payback for the Democrats' past opposition to Republican nominees.

Republicans portrayed Caitlin Halligan as a liberal activist, while Democrats argued she had outstanding qualifications for the seat that has been vacant since John G. Roberts Jr. was elevated to the Supreme Court in 2005.

The vote was 54-45, short of the 60 votes needed under Senate rules to break a filibuster. Only one Republican, Lisa Murkowski of Alaska, voted in favor of allowing the nomination to move to a final floor vote, though she said she would not have supported Halligan's confirmation.

Halligan, 44, is general counsel in the Manhattan District Attorney's Office and former New York State solicitor general.

GOP opposition reignited the debate over judicial nominations, just as the issue had appeared to slightly calm down. Since September, the Senate confirmed five Obama appellate nominees, four unanimously, and 19 U.S. district judges.

Obama, in a statement, said he was "deeply disappointed" with the "Republican pattern of obstructionism that puts party ahead of country." Senate Republicans, he said, "are blocking 20 other highly qualified judicial nominees, half of whom I have nominated to fill vacancies deemed 'judicial emergencies' by the Administrative Office of the Courts."

In May, Democrats fell short of the 60 votes needed to end a filibuster against Goodwin Liu as Obama's nominee for the San Francisco-based Ninth Circuit appeals court. Liu is now on the California Supreme Court.

Sen. Charles E. Grassley of Iowa, the ranking Judiciary Committee Republican, said "there is a lot at stake with nominations" to the D.C. Circuit, as its judges have frequently been considered - and elevated - to the U.S. Supreme Court.

Grassley then launched into the partisan history of the Republican attempt to fill the seat after Roberts vacated it. President George W. Bush in June 2006 nominated Peter Keisler, who was a top Justice Department official.

"Mr. Keisler waited 918 days for a committee vote, which never came," Grassley said. He said six of Bush's nominees, including Roberts, endured "delays, filibusters, multiple hearings, and other forms of obstruction."

He contended that Halligan signed a report by New York City's bar association panel that objected to military detentions of suspected terrorists. Grassley said Halligan had a role in state lawsuits "attempting to hold handgun manufacturers liable for criminal acts committed with handguns."

Sen. Charles E. Schumer (D., N.Y.) said this filibuster was likely the final blow to a 2005 agreement by 14 senators to filibuster judicial nominees only under extraordinary circumstances.