(Recasts, adds McCain)
By David Alexander and Paul Eckert
WASHINGTON, March 24 (Reuters) - President George W. Bush expressed sorrow on Monday as the number of U.S. troops killed in Iraq hit 4,000, days after he marked the fifth anniversary of the unpopular war.
"One day people will look back at this moment in history and say ‘thank God there were courageous people willing to serve’ because they laid the foundation for peace for generations to come," Bush said after a roadside bomb killed four U.S. soldiers, pushing the toll to the new milestone.
Recent opinion polls show around 60 percent of U.S. voters disapprove of Bush’s handling of the war and roughly the same number believe the loss of American life was not worthwhile.
Last week, on the fifth anniversary of the U.S.-led invasion, the Republican president said the United States was on track for victory.
Democratic presidential contenders Barack Obama and Hillary Clinton praised the heroism of U.S. troops while promising that if elected they would come home.
Obama said the war should never have been waged and troops should be brought home soon. Clinton pledged to respond "by bringing a responsible end to this war, and bringing our troops home safely."
Presumptive Republican presidential nominee John McCain, who has said U.S. troops could remain in Iraq for 100 years, told a veterans’ group in Chula Vista, California, that his thoughts and prayers go out to families of troops killed in the war "every day, not just on the day that 4,000 brave young Americans are sacrificed."
After a State Department briefing with Secretary of State Condoleezza Rice, Bush, who will leave office in January, offered words of comfort for the families of the troops killed in Iraq.
PRAY FOR COMFORT AND STRENGTH
"I hope their families know that citizens pray for their comfort and strength, whether they were the first one who lost their life in Iraq or recently lost their lives in Iraq," he told reporters.
Pentagon spokesman Bryan Whitman said: "Every single loss of a soldier, sailor, airman and Marine is keenly felt by us in the department, by military commanders, by families, friends, both in theater and here at home."
Precise Iraqi casualties are not known but the widely cited human rights group Iraq Body Count said this month that up to around 89,300 civilians have been killed since 2003.
The war has cost the United States $500 billion.
The president chaired a meeting of his National Security Council on Monday and was briefed by Ryan Crocker, the U.S. ambassador in Baghdad, and Gen. David Petraeus, the top U.S. military officer in Iraq.
Bush and his advisers are trying to decide whether to continue to reduce troop levels in Iraq after last year’s increase, which is credited with lowering violence there.
Some experts are urging a pause in troop reductions to avoid losing the gains made in recent months.
The deaths that pushed the U.S. toll in Iraq to 4,000 happened as new violence burst out, including sustained mortar fire against the U.S.-protected "Green Zone" in Baghdad.
Whitman said that despite the new casualties, violence overall was down compared to last year.
"Both coalition and Iraqi security force casualties are down significantly from about May of ‘07," he said. "Iraqi civilian casualties has also been on a downward trend since December of ‘06."
"Would we like to reduce the casualties to nothing? Of course we would. Are there still going to be casualties in the days ahead? Most unfortunately there will be." (Additional reporting by Kristin Roberts, Jeff Mason and Tim Gaynor; editing by Mohammad Zargham)