The United States must be prepared to fight the war on terror for decades to bring peace to Iraq and the rest of the Middle East, Vice President Dick Cheney (search) said Wednesday.

"Like other great duties in history, it will require decades of patient effort, and it will be resisted by those whose only hope for power is through the spread of violence," said Cheney. "As the people of that region experience new hope, progress, and control over their own destiny, we will see the power of freedom to change our world and a terrible threat will be removed."

Cheney did not specify how long he believes U.S. troops will have to stay in Iraq, just as other administration officials have avoided providing a timetable. Some military commanders have expressed hopes that substantial American withdrawals could begin next spring or summer, though they have edged away from such comments in recent days.

Speaking to the Association of the U.S. Army, Cheney joined the chorus of Bush administration officials — including the president — who have tried in recent days to bolster an American public that has grown increasingly weary of the war in Iraq. He told the audience filled with military members that the only way terrorists can win is if the United States "lost our nerve and abandoned our mission."

He also echoed Bush administration assertions that Iraqi security forces are growing, and are increasingly able to take charge. His comments come just a week after the top commander in Iraq told Congress that the number of Iraqi army battalions capable of fighting without U.S. help had dropped from three to one.

"One of the challenges we faced was that after clearing out terrorists, there weren't always enough trained Iraqi forces to retain control," Cheney said. Now, he said, Iraqi forces control more parts of the country than at any time in the past two years.

Later at the Pentagon, Army Lt. Gen. David Petraeus (search), who spent the past year overseeing the training of Iraqi forces, said recent public discussion about the combat readiness of Iraq forces had missed an important point: that in addition to the single Iraqi battalion that is capable of operating fully independent of U.S. troops, there are more than 36 army and special police combat battalions that are only slightly less capable.

Petraeus said those battalions can take the leading role in a fight, albeit with U.S. support. He said the number of such battalions is higher than 36 but declined to be precise, saying the exact number is classified secret.

Petraeus, who finished his assignment in Iraq on Sept. 8, told reporters that the total number of Iraqi army and special police battalions is slightly more than 115, of which just one is at a "level 1" rating, meaning it can operate fully independent of U.S. forces.

More than 36 battalions, or roughly 28,000 Iraqi police and soldiers, are rated at "level 2," and more than 80 battalions, or roughly 64,000 police and soldiers, are at "level 3." The level 3 rating means they are deemed capable of engaging in combat, alongside U.S. troops.