The latest death came during one of the most violent periods during which the Pentagon says hate and revenge killings between Iraq's sects are now a bigger security problem than ever.
The death of a Texas soldier, announced Sunday by the Pentagon, raised the number of U.S. military deaths in Iraq to at least 3,000, according to an Associated Press count, since the war began in March 2003.
Spc. Dustin R. Donica, 19, of Spring, Texas, was killed by small arms fire in Baghdad late last week. The announcement caps the deadliest month for U.S. forces in Iraq in the past year.
"The hardest decision the president ever has to make is to send our men and women into harm's way," said White House Deputy Press Secretary Scott Stanzel, with Mr. Bush in Crawford, Texas. "The president believes that every life is precious and grieves for each one that is lost. He will ensure their sacrifice was not made in vain."
In other developments:
President Bush is struggling to salvage a military campaign that, more than three-and-a-half years after U.S. forces overran the country, has scant support from the American public. In large part because of that discontent, voters gave Democrats control of the new Congress that convenes this week. Democrats have pledged to focus on the war and Bush's conduct of it.
Three thousand deaths are tiny compared with casualties in other protracted wars America has fought in the last century. There were 58,000 Americans killed in the Vietnam War, 36,000 in the Korean conflict, 405,000 in World War II and 116,000 in World War I, according to Defense Department figures.
Even so, the steadily mounting toll underscores the relentless violence that the massive U.S. investment in lives and money — surpassing $350 billion — has yet to tame, and may in fact still be getting worse.
A Pentagon report on Iraq said in December that the conflict now is more a struggle between Sunni and Shiite armed groups "fighting for religious, political and economic influence," with the insurgency and foreign terrorist campaigns "a backdrop."
From mid-August to mid-November, the weekly average number of attacks in the country increased 22 percent from the previous three months. The worst violence was in Baghdad and in the western province of Anbar, long the focus of activity by Sunni insurgents, said a December report.
Though U.S.-led coalition forces remained the target of the majority of attacks, the overwhelming majority of casualties were suffered by Iraqis, the report said.
The American death toll was at 1,000 in September of 2004 and 2,000 by October 2005.
Mr. Bush told an end-of-the-year press conference that the deaths distress him.
"The most painful aspect of the presidency is the fact that I know my decisions have caused young men and women to lose their lives," the president said.
"We will be fighting violent jihadists for peace and security of the civilized world for years to come. The brave men and women of the U.S. military are fighting extremists in order to stop them from attacking on our soil again," Stanzel said.
Mr. Bush was spending the holiday weekend at his Texas ranch.
In an interview on Dec. 21 with The Associated Press, Secretary of State Condoleezza Rice said the war was "worth the investment" in American lives and dollars.
In his strategy reassessment, President Bush has consulted Iraqis, his uniformed and civilian advisers, an outside bipartisan panel that studied the failing war, and other defense and foreign policy experts. New Defense Secretary Robert Gates journeyed to Iraq in his first week on the job in December to confer with American commanders and Iraqi leaders.
Among the president's options was a proposal to quickly add thousands of U.S. troops to the 140,000 already in Iraq to try to control escalating violence in Baghdad and elsewhere.
Others believe too much blood and money already have been sacrificed. Democrats have wanted Bush to move toward a phased drawdown of forces, while the bipartisan Iraq Study Group recommended removing most U.S. combat forces by early 2008 while shifting the U.S. role to advising and supporting Iraqi units.
Having launched the war against the advice of a number of nations, the Bush administration never got a huge international contribution of troops, meaning foreign forces helping the Iraqis are overwhelmingly American.
The death toll shows it. As of late December, the British military has reported 126 deaths in the war so far; Italy, 33; Ukraine, 18; Poland, 18; Bulgaria, 13; Spain, 11; and Denmark, six. Several other countries have had five or less.