Washington ? President Bush said Tuesday that American forces will remain in Iraq for years and it will be up to a future president to decide when to bring them all home. But defying critics and plunging polls, he declared, “I’m optimistic we’ll succeed. If not, I’d pull our troops out.”

The president rejected calls for the resignation of Defense Secretary Donald Rumsfeld, chief architect of wars in Iraq and Afghanistan. “Listen, every war plan looks good on paper until you meet the enemy,” Bush said, acknowledging mistakes as the United States was forced to switch tactics and change a reconstruction strategy that offered targets for insurgents.

He also rejected assertions by Iraq’s former interim prime minister that the country had fallen into civil war amid sectarian violence that has left more than 1,000 Iraqis dead since the bombing last month of a Shiite Muslim shrine.

“This is a moment the Iraqis had a chance to fall apart and they didn’t,” Bush said, crediting religious and political leaders with restraint.

The president spoke for nearly an hour at a White House news conference, part of a new offensive to ease Americans’ unhappiness with the war and fellow Republicans’ anxiety about fall elections. He faced skeptical questions about Iraq during an appearance Monday in Cleveland, and plans another address soon on Iraq.

Public support for the war and for Bush himself has fallen in recent months, jeopardizing the political capital he claimed from his 2004 re-election victory. “I’d say I’m spending that capital on the war,” Bush said.

Members of President Bush's senior staff, from left, press secretary Scott McClellan, deputy chief of staff Karl Rove and counselor to the president Dan Bartlett listen to a reporter ask President Bush a question at a news conference at the White House. President Bush said Tuesday there will be more

The White House believes that people appreciate Bush’s plainspoken approach even if they disagree with his decisions.

“I understand war creates concerns,” the president said. “Nobody likes war. It creates a sense of uncertainty in the country.”

Bush has adamantly refused to set a deadline for the withdrawal of U.S. forces from Iraq. Asked if there would come a day when there would be no more U.S. forces in Iraq, Bush said, “That, of course, is an objective. And that will be decided by future presidents and future governments of Iraq.”

Pressed on whether that meant a complete withdrawal would not happen during his presidency, Bush said, “I can only tell you that I will make decisions on force levels based upon what the commanders on the ground say.”

White House officials worried Bush’s remarks would be read as saying there would not be significant troop reductions during his presidency. They pointed to comments Sunday by Gen. George Casey, commander of U.S. forces in Iraq, who said he expected a substantial troop reduction “certainly over the course of 2006 and into 2007.”

The Pentagon announced in December that U.S. force levels would be reduced from the baseline figure of about 138,000 to about 131,000 by the end of March. The total currently is 133,000. In late February the Pentagon told Congress that “it will be possible to consider” additional reductions as the political process moves forward and as Iraqi security forces gain experience. No timetable has been set for deciding on additional cuts.

More than 2,300 American troops have died in Iraq. At home, nearly four of five people, including 70 percent of Republicans, believe civil war will break out in Iraq, according to a recent AP-Ipsos poll.

“I am confident – I believe, I’m optimistic we’ll succeed,” the president said. “If not, I’d pull our troops out. If I didn’t believe we had a plan for victory I wouldn’t leave our people in harm’s way.”

Bush said U.S. forces were essential for the stability of Iraq and restraining al-Qaida in the Middle East.

“Their objective for driving us out of Iraq is to have a place from which to launch their campaign to overthrow moderate governments in the Middle East, as well as to continue attacking places like the United States,” he said.