DENVER (Reuters) - President Bush on Wednesday will compare his administration's war on terror to World War II and cast the Middle East as a critical front akin to war-time Europe, during a commencement address at the U.S. Air Force Academy, a senior White House official said.

A day after he embraced a new Iraqi interim government as a step toward representative government, the Republican president was also expected to speak in detail about America's enemies such as Osama bin Laden's al-Qaeda network, said the official, who spoke on condition of anonymity.

"He'll say we're fighting the broader war on terror throughout the world, but much like in World War II, when Europe became the critical front in that war, the greater Middle East is the critical front in the war on terror," the official said.

"Events in Europe determined the Cold War; this is kind of the equivalent of that in the Middle East," he added.

Bush has repeatedly held out the prospect of a democratic Iraq as a catalyst for spreading political and economic reform across the region through his Greater Middle East Initiative, which he will push at next week's Group of Eight summit during meetings with Western and Arab leaders.

The initiative has angered many Arabs who view it as a system of Western-imposed reforms. But that has not stopped Bush from reiterating calls for greater regional "freedom."

"The world is counting on our country to lead the cause of freedom and peace," he told supporters at a Republican fund-raiser in Denver late on Tuesday. "This is the work that history has set before us."

U.S. INTENTIONS

The Air Force Academy speech in Colorado Springs is billed as a follow-up to Bush's address at the Army War College a week ago in which he discussed U.S. intentions for bringing democracy to Iraq, beginning with a scheduled June 30 handover of authority.

"The president's speech is going to focus in the most detail yet on the nature of the enemy we face in the broader war on terror -- why ... this kind of clash of ideologies is a defining moment for our country and the civilized world, much like it was in World War II," the White House official said.

Bush, who is in a tight election year battle against Democratic presidential candidate John Kerry, has seen his job approval ratings slump to new lows amid public concerns about U.S. involvement in Iraq, where more than 800 American soldiers have died since a March 2003 invasion that U.S. officials once likened to the Allied invasion of Europe.

Undeterred by political pressure, the president has donned the mantel of war president by vowing to keep U.S. troops in Iraq until the country is stable and mounting a series war-related speeches that will include a June 6 appearance at the site of the 1944 Normandy invasion.

His Wednesday speech was expected to touch on U.S. efforts in four areas: the disruption and dismantling of militant groups; assistance to governments beset by militant violence such as the Philippines and Afghanistan; enhanced curbs against the proliferation of weapons of mass destruction; and the promotion of Middle East reform as a buffer against militancy.

The president's speech was expected to get under way at the Air Force Academy shortly after 1 p.m. EDT (1700 GMT).