WASHINGTON (CNN) -- Frustrated by Republican efforts to block votes on bringing American combat troops home from Iraq, Senate Democratic leaders rolled out sleeping cots Tuesday for an all-night debate on the war.
"We're going to continue working on this until we get a vote on this amendment," said Democratic Majority Leader Harry Reid.
Democratic Senate Majority Leader Harry Reid called the overnight session to highlight a GOP filibuster preventing the Senate from voting on an amendment to the Defense Authorization bill that would bring U.S. combat troops home by next spring.
"Republicans are using a filibuster to block us from even voting on an amendment that could bring the war to a responsible end," Reid said on the Senate floor Tuesday after Republicans had blocked a request for unanimous approval of the measure.
"They are protecting the president rather than protecting our troops. They are denying us an up-or-down -- yes or no -- vote on the most important issue our country faces.
"We have no choice but to stay in session to continue speaking out on behalf of our troops and all Americans, to continue requesting consent for an up-or-down vote on our amendment to end the war."
In a letter to Senate Minority Leader Mitch McConnell, Reid said he wanted votes on three other amendments in addition to Levin-Reed -- measures sponsored by Republican Sens. Richard Lugar and John Warner; Democratic Sen. Ken Salazar and GOP Sen. Lamar Alexander; and Democratic Sen. Ben Nelson and Republican Sen. Susan Collins.
The Levin-Reed amendment calls for U.S. combat troops to return from Iraq by April 30, 2008. Lugar-Warner requires the administration to come up with contingency plans, including a possible withdrawal, that could be set into motion by the end of the year.
Salazar-Lamar would make the recommendations of the Iraq Study Group the basis for future U.S. policy in Iraq.
Nelson-Collins sets a March 31, 2008, goal for shifting U.S. soldiers out of Baghdad, focusing troops' work instead on battling insurgents in Anbar province and al Qaeda.
Although she strongly supports a change in policy in Iraq, Collins told CNN that she is undecided on whether to vote for Levin-Reed, adding that "cheap political stunts" like the all-night session are not designed for "serious debate." 
Watch workers roll in sleeping cots to prepare for debate »
"I'm undecided because I very much want a change in mission," she said. "I think that's long overdue. The president's strategy has not been successful, and we need to pursue a new course. But I'm very concerned about mandating exactly when troops need to be withdrawn no matter what the circumstances and no matter what the consequences."
"This all-night debate has no impact on me whatsoever," she said. "It's clearly not an opportunity for a serious debate. ... We don't have to stay in all night to have a serious debate on Iraq. We can do that in the daylight hours just fine."
McConnell, speaking earlier in the day, denied that Republicans were trying to prevent the Senate from voting on the measures.
"I'd like to point out that these are votes that frankly we could have had at any point," McConnell said at a news conference. "We've offered to have the vote today. We offered to have the vote at any point."
"The definition of filibuster is trying to prevent a vote. We're anxious to have the vote. If they want to debate all night, we'll be here," he said. "We're optimistic that we're going to prevail on the Levin-Reed proposal."
"The Democrats unfortunately are trying to undermine the efforts of our troops and restrict the ability of our generals to carry out their mission."
Sixty votes are required to stop debate and move the proposal to the floor, and Democrats admit they don't have enough Republican support to break the filibuster -- the Senate's tradition of unlimited debate.
Only three GOP senators -- Chuck Hagel of Nebraska, Olympia Snowe of Maine and Gordon Smith of Oregon -- have said they will vote with the Democrats on Levin-Reed. And Bush vetoed an earlier call for a withdrawal of American combat troops in May.
Republican Sen. John McCain of Arizona, a presidential contender, said withdrawing troops would undercut U.S. military progress in Iraq.
"No lasting political settlement can grow out of a U.S. withdrawal," said McCain. "On the contrary, a withdrawal must grow out of a political solution -- a solution made possible by the imposition of security by coalition and Iraqi forces."
Meanwhile, a Democratic presidential hopeful announced Wednesday that he would introduce an amendment to the defense authorization bill that would cut funding for combat missions in Iraq -- taking up a frequent Republican challenge for Democrats who oppose the 4-year-old war to use congressional control of the nation's finances to bring it to an end.
Sen. Christopher Dodd of Connecticut said he would use the billions in savings to rebuild the nation's military.
"Millions of dollars a week are being squandered in Iraq ... while our nation's military is calling out for additional resources to repair the damage caused by the administration's policies," Dodd said.
A Congressional Research Service report in June estimated the cost of the war in Iraq at nearly $10 billion a month, or about $2.3 billion a week.
Dodd said the National Guard has requested $38 billion from Congress to replace vehicles, aircraft, equipment and personal gear that were transferred to Iraq, and that shortfall remains unfunded in the current defense authorization bill.
"It means that we are short of equipment to respond to natural and man-made disasters here at home, short of equipment for training, short of equipment to maintain the standard of maintenance rotation for equipment currently in the field ... short of equipment to protect the American people," he said.
Dodd said the Air Force needs $16 billion for radar systems and cargo aircraft; the Army needs $10 billion for specially armored trucks, night vision goggles and bomb disposal gear; and the Navy needs $5.6 billion for helicopters and maintenance.
"This administration has taken its eye off the ball," Dodd said. "Nearly six years after the 9/11 attacks, the war is its only focus. It's made the U.S. far more vulnerable, in my view, as a result." E-mail to a friend 
CNN's Dana Bash contributed to this report.
All About U.S. Senate • Iraq War
Read
VIDEO
INTERACTIVE
From the Blogs: 
Sit tight, we're getting to the good stuff
