President Bush, accompanied by Secretary of State Condoleezza Rice, makes a statement at the State Department in Washington. Bush on Monday offered his sympathies to the families of the 4,000 military personnel killed in Iraq.

Washington ? Marking a grim milestone, a determined President Bush declared Monday the lives of 4,000 U.S. military men and women who have died in Iraq “were not lost in vain.” The White House signaled anew that additional troops won’t be pulled out soon.

A roadside bomb in Baghdad killed four U.S. soldiers Sunday night, pushing the death toll to 4,000.

That number pales compared with those of other lengthy U.S. wars, but it is much higher than many Americans, including Bush, ever expected after the swift U.S. invasion of Iraq five years ago.

Bush proclaimed the end of major combat operations in Iraq in May 2003. Almost all of the U.S. deaths there have happened since then.

“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 foundations for peace for generations to come,”‘ Bush said after a State Department briefing about long-term diplomacy efforts.

“I have vowed in the past, and I will vow so long as I’m president, to make sure that those lives were not lost in vain – that, in fact, there is an outcome that will merit the sacrifice,” Bush said.

The news of 4,000 dead in Iraq came the week after the war rolled into its sixth year, dominating most of Bush’s presidency. Almost 30,000 U.S. service members have been wounded in the war.

Early in April, Bush is expected to announce the next steps in the war, and he is likely to embrace a pause in any troop withdrawals beyond those scheduled to end this July.

Democrats in Congress and on the presidential campaign trail continue to push for a faster end to war. But Bush still has the upper hand for 10 months.

“Americans are asking how much longer must our troops continue to sacrifice for the sake of an Iraqi government that is unwilling or unable to secure its own future,” said House Speaker Nancy Pelosi. She said the cost to the U.S. reputation is immense, and the threat to the economy at home is unacceptable.

Senate Majority Leader Harry Reid said the death toll is a reminder that the nation must get out of an “endless civil war and make America more secure.”

The White House was careful in its reaction to the milestone, calling it a sober moment but emphasizing that deaths are grieved no matter what the number. Bush said people are praying for the families of those killed whether they were among the first or the most recent casualties.

Grim milestones such as new death toll often go unremarked by Bush. But he chose on this occasion to note the losses, albeit briefly and without taking questions from reporters.

As always, his message was determination.

“Our strategy going forward will be aimed at making sure that we achieve victory and, therefore, America becomes more secure,” he said. Just last week, Bush said the high cost in lives and money was necessary to halt the spread of terrorism and keep Iraq out of chaos.

The White House said Bush is likely to embrace an expected recommendation from his top commander in Iraq, Gen. David Petraeus, for a halt in troop withdrawals in July. During the pause, Petraeus and other senior commanders would make yet another assessment of conditions in Iraq, possibly in September, before recommending any specific troop reductions for the final months of 2008.