Senate Republicans have blocked a bid by Democrats to give US troops in Iraq more home leave - a plan strongly opposed by the Bush administration.
It was the latest defeat for Democrats in Congress over Iraq
The Democrats wanted US troops to have time off between tours in Iraq equal to their 15-month deployments.
The measure needed 60 votes to pass in the Democratic controlled Senate but received only 56 votes with 44 against.
US Defence Secretary Robert Gates called it a backdoor attempt to pull troops off the battlefield.
He warned that he would have recommended US President George W Bush veto the measure had it passed.
The BBC's Rajesh Mirchandani in Washington said the bill had been the Democrats' best chance this year of changing the course of US strategy in the Iraq war.
Republican Senators who were dubious over the president's policy are now giving him more time after an upbeat assessment last week of progress in Iraq by the top US commander in Iraq, Gen David Petraeus, our correspondent says.
Supporters of the bill, which was also narrowly defeated in July, said opponents were ignoring the troops' interests.
"In blocking this bipartisan bill, Republicans have once again demonstrated that they are more committed to protecting the president than protecting our troops," Senate Majority leader Harry Reid said.
Senator Chuck Hagel, one of six Republicans who backed the bill, said: "We cannot continue to look at war and the people who fight and die in wars as abstractions, as pawns, as objects."
But critics said it would have interfered with Mr Bush's plans to reduce US troop levels in Iraq by around 30,000 to about 130,000 by mid-2008.
US troops currently have about 12 months rest at home between deployments.
Republican Senator John McCain, a presidential candidate next year, branded the bill "dangerous".
And fellow Republican Jim Bunning said of the Democrats' motion: "I will not support this slow bleed strategy in Iraq. It ties the hands of our commanders."
It was the latest defeat over the conflict for Democrats, who grabbed control of Congress last year.
They have at least two more proposals on Iraq to come, including explicit calls for combat troop withdrawals, but analysts say these are also likely to fail.