The first plan, which would require a troop pullout within the next year, lost by a vote of 86-to-13. The second, which set no timetable, was defeated by a 60-to-39 vote.
At times the Senate debate was serious and sober on a war that has taken more than 2,500 American lives, reports CBS News correspondent Bob Fuss. But there has also been a lot of political sniping – Republicans accusing Democrats of encouraging "surrender" or "cut and run," and Democrats saying the Republicans are using the war for their own re-election efforts.
"Withdrawal is not an option. Surrender is not a solution," declared Senate Majority Leader Bill Frist of Tennessee, who characterized Democrats as defeatists wanting to abandon Iraq before the mission is complete.
Senate Democratic leader Harry Reid of Nevada, in turn, portrayed Republican leaders as blindly following President Bush's "failed" stay-the-course strategy. "It is long past time to change course in Iraq and start to end the president's open-ended commitment," he said.
The votes came a week after both houses of Congress soundly rejected withdrawal timetables for the 127,000 troops in Iraq and as polls show voters are weary about the war in its fourth year.
Republicans argued the United States must stay put to help the fledgling Iraqi government, while Democrats demanded that the Bush administration make clear that American forces won't be in Iraq forever.
"We must give them that support and not send a signal that we're going to pull possibly the rug out from under them," Sen. John Warner, R-Va., said.
"The United States, with our Iraqi partners, has the responsibility to see this through," Sen. John McCain, R-Ariz., added.
But Sen. Russ Feingold, D-Wis., said: "It is time to tell the Iraqis that we have done what we can do militarily."
"Maintaining the status quo is a recipe for continuing instability and failure," Sen. Carl Levin, D-Mich., said.
Republicans and Democrats on Capitol Hill have staged bitter partisan debates on Iraq for two weeks, with both sides maneuvering for the political upper-hand in a midterm election year.
This week, Senate Republicans welcomed the Democratic-engineered debate because it highlighted divisions in the Democratic Party little more than four months before Election Day and as the GOP is trying to overcome polls showing the public favors a power shift in Congress to Democrats.
Democrats, for their part, tried to deflect attention from differences in their party on Iraq, even though the debate was over two separate Democratic proposals on the fate of U.S. troops.
The first proposal, sponsored by Feingold and Sen. John Kerry of Massachusetts, would require the administration to withdraw all combat troops from Iraq by July 1, 2007.
The other proposal — which most Democrats and their leadership support — calls for the administration to begin "a phased redeployment of U.S. forces" by year's end. The nonbinding resolution would not set a deadline of when all forces must be withdrawn.
The Bush administration says U.S. troops will stay in Iraq until Iraqi security forces can defend the country against a lethal insurgency that rose up after the U.S.-led invasion in 2003 that toppled dictator Saddam Hussein.
Senate Republicans opposed any timeline. They said a premature pullout and a public pronouncement of any such plan would risk all-out civil war, tip off terrorists, threaten U.S. security and cripple the Iraqi government just as democracy is taking hold.
In turn, almost all Democrats chastised Republicans for walking in lockstep with Mr. Bush and they accused him of failing to articulate a plan for the way ahead in Iraq. Democrats said it is time for troops to start coming home and for Congress to send a clear signal that the U.S. presence is not indefinite.
Sensitive to talk of a divided party, Democratic aides circulated a memo from a Democratic pollster suggesting that Republicans will pay a price in November for standing with the president's war policies. But Republicans dismissed that notion.
Democrats also played down concerns, voiced privately by some party strategists, that the Kerry-Feingold call for a "hard-and-fast" deadline is hindering the party's efforts to project a unified position on Iraq for the fall.