As anti-war protesters prepare for a rally that could draw tens of thousands of people to the nation’s Capitol this weekend, President Bush (search) defended his position on Thursday to keep American forces in Iraq.

“Some Americans want us to withdraw our troops so that we can escape the violence. And I recognize their good intentions but their position is wrong,” Bush said. "For the safety and security of the American people, that's not going to happen on my watch."

Bush said the "costly mistakes of the past that led to the attacks of Sept. 11, 2001," allowed terrorists to believe that the nation was vulnerable.

“The terrorists concluded that we lacked the courage and character to defend ourselves. And so they attacked us. And now the terrorists are testing our will and resolve in Iraq," he said.

Attacks on America prior to Sept. 11, 2001, include the hostage crisis in Iran, the bombing of the U.S. Marines barracks in Lebanon (search), the killing of American soldiers in Somalia, the destruction of two U.S. embassies in Africa and the first terrorist attack on the World Trade Center in 1993, Bush said.

Bush spoke at the Pentagon after a briefing on Iraq and Afghanistan (search) by Gen. George Casey, the top commander in Iraq, and Gen. John Abizaid, the commander of the U.S. Central Command.

Vice President Dick Cheney (search), Secretary of Defense Donald Rumsfeld, Secretary of State Condoleezza Rice and Chairman of the Joint Chiefs of Staff Richard B. Myers attended.

Bush said he knew American lives were being sacrificed in Iraq with more than 1,900 dead but added that "we'll honor their sacrifice by completing the mission and winning the war on terrorism."

Meanwhile, anti-war protesters arrived in Washington on Wednesday for preparations for Saturday’s rally.

Anti-war activist Cindy Sheehan (search), who led a three-week cross-country bus tour that began near President Bush’s ranch in Crawford, Texas, began protest speeches outside the White House and Capitol.

On Thursday, Sheehan, whose 24-year-old son, Army Spc. Casey Sheehan, was killed last year in Iraq, was meeting Thursday with Senate Majority Leader Bill Frist, R-Tenn.

Earlier in the day, the protest group Win Without War announced a print ad campaign that refers to the conflict in Iraq and points to Bush administration officials, saying "They Lied" then lists the names of all the slain soldiers, saying "They Died."

Regardless of people's position on the issue, U.S. focus on the War on Terror remains on Iraq as that nation moves toward elections in October and December.

This week’s parliamentary elections in Afghanistan were a step toward democracy, Bush said. Earlier this week, Rumsfeld called the elections a historic step.

"The country that hosted Usama bin Laden, that supported training camps for Al Qaeda, endured decades of civil war, Soviet occupation, drought, Taliban brutality, is now a democracy that fights terrorists instead of harboring them," Rumsfeld said.

“Our country will stand with the Afghan people as they secure their freedom and become an ally in the War on Terror,” Bush said.

As for Iraq, Bush said the growing number of Iraqis being trained in basic security operations is helping ease the burden on American forces. A larger Iraqi force helps American forces to move on to other targets, he said.

“The growing size and increasing capabilities of the Iraqi security forces are helping our coalition deal with a challenge we have faced since the beginning of the war."

The Associated Press contributed to this report.