WASHINGTON – Democrats forced the Senate into a rare closed-door session yesterday for an inquiry into the Bush administration’s handling of intelligence about Iraq’s weapons in the run-up to the war.

With no warning in the mid-afternoon, the Senate’s top Democrat invoked the little-used Rule 21, which forced aides to turn off the chamber’s cameras and close its massive doors after evicting all visitors, reporters, and most staffers. Plans to bring in electronic bug-sniffing dogs were dropped when it became clear that senators would trade barbs but discuss no classified information.

Republicans condemned the Democrats’ maneuver, which marked the first time in more than 25 years that one party had insisted on a closed session without consulting the other party. But within two hours, Republicans appointed a bipartisan panel to report on the progress of a Senate Intelligence Committee report on pre-war intelligence, which Democrats say has been delayed for nearly a year.

“Finally, after months and months and months of begging, cajoling, writing letters, we’re finally going to be able to have Phase II of the investigation regarding how the intelligence was used to lead us into the intractable war in Iraq,” Minority Leader Harry Reid, a Democrat of Nevada, told reporters, claiming a rare victory for Democrats in the GOP-controlled Congress.

Beneath the political pyrotechnics was an issue that has infuriated liberals but flummoxed many Democratic lawmakers who voted three years ago to approve the war: allegations that administration officials exaggerated Iraq’s weapons capabilities and terrorism ties, and then resisted inquiries into the intelligence failures. Friday’s indictment of top White House aide I. Lewis “Scooter” Libby on perjury and obstruction charges gave Democrats a new opening to demand that more light be shed on these issues, including administration efforts to discredit a key critic of the prewar claims of Iraq’s weapons of mass destruction.

Democrats were dismayed that President Bush made no apologies after the indictment and that his naming of a new Supreme Court nominee Monday knocked the Libby story off many front pages. As he stood on the Senate floor to demand the closed session – a motion not subject to a vote under the rule – Mr. Reid said Mr. Libby’s grand jury indictment “asserts this administration engaged in actions that both harmed our national security and are morally repugnant.”

The usually unflappable Majority Leader Bill Frist, a Republican of Tennessee, was searching for words to express his outrage to reporters a few minutes later. The Senate “has been hijacked by the Democratic leadership,” he said. “They have no convictions, they have no principles, they have no ideas.” Never before, he said, had he been “slapped in the face with such an affront … For the next year and a half, I can’t trust Senator Reid.”

Mr. Frist seemed much calmer when the closed session ended. He agreed to a six-senator, bipartisan task force that will report by November 14 on “the intelligence committee’s progress of the Phase II review of the pre-war intelligence and its schedule for completion.”

Committee Chairman Pat Roberts, a Republican of Kansas, said the report was nearing completion anyway, but Democrats disputed the claim. Committee Vice Chairman Jay Rockefeller, a Democrat of West Virginia, began inquiring about the evidence against Iraq one week before American troops invaded in March 2003. His interest was sparked by revelations that the Bush administration gave forged documents to U.N. weapons inspectors in support of claims that Iraq had sought to buy a key ingredient for nuclear weapons from the West African nation of Niger.

Mr. Roberts resisted a full investigation for three months. But in June 2003, when it became increasingly ap parent that no weapons of mass destruction were being found in Iraq, the committee agreed to look into the intelligence cited in the administration’s case for war. In February 2004, senators agreed to a second phase that would investigate the Bush administration’s use of intelligence and examine public statements made by key policymakers about the threat posed by Iraq.