President Bush on Saturday sought to marshal the nation's resolve to withstand more casualties, saying further sacrifice must be expected with U.S.-led troops "now fighting the most desperate units" of the Iraqi army.

Despite stronger-than-expected fighting in Iraq's south and more deaths of American and British troops, Bush was steadfastly optimistic about the war's outlook. He was spending the second weekend of the invasion, like the first, at Camp David.

"The fighting is fierce and we do not know its duration, yet we know the outcome of this battle," the president said in his weekly radio address. "The Iraqi regime will be disarmed and removed from power."

Bush planned a video conference with his war council from the Maryland mountain retreat Saturday morning.

Speaking Friday at a White House tribute to veterans' groups, Bush braced the nation for more casualties as part of an administration-wide campaign to lower expectations for a quick, mostly risk-free war.

He also assured Americans the war was going well, even as administration officials privately conceded that Iraqi tactics had forced changes in U.S. battlefield strategies.

During that East Room appearance, and the almost word-for-word repeat of those remarks in his radio address, Bush issued a stern warning to Iraqi commanders.

Hoping to rally Americans behind the war, he intensified criticism of Saddam Hussein's regime. He said the regime was murdering Iraqis who refuse to fight coalition forces, executing prisoners of war, opening fire under the guise of surrender, and hanging an Iraqi woman for waving at coalition troops.

Senior administration officials, speaking on condition of anonymity, said U.S. forces are collecting and cataloging evidence of war crimes. The United States will prosecute those cases, the officials said, though no decision has been made on whether to use the military justice system or traditional court trials.

U.S. prosecutions will not include prewar crimes, an area that will be left to the next Iraqi government, the officials said.

Bush has previously warned Iraqi commanders that they will be treated as war criminals if they use chemical or biological weapons against U.S. troops. He said he expects such war crimes to occur given the nature of Saddam's regime.