By stressing al-Qaida's burgeoning operation in Iraq, Bush again aimed to frame the war in the public's mind as a matter of protecting the United States. Yet the war itself has turned into a valuable recruiting tool for al-Qaida, senior intelligence officials concede.

US President Bush walks up the stairs as he boards Air Force One, Tuesday, July 24, 2007, at Andrews Air Force Base in Maryland, prior to traveling to Charleston, S.C.[AP]

Bush is up against highly skeptical audiences with 18 months left in office. The public has largely lost faith in the war, Congress is weighing ways to end it, and international partners have fading memories of the 2001 attacks against the US

In an afternoon speech to military personnel, Bush will warn that al-Qaida anywhere remains a catastrophic threat to the US, nowhere more so than from its base in Iraq.

Bush declassified information about al-Qaida's operation for his speech. His goal is to show that al-Qaida in Iraq is a core part of the overall terror network _ a direct jab at those who say US troops in Iraq are bogged down against the wrong enemy.

For his setting, Bush chose Charleston Air Force Base, a vital launching point for cargo and military personnel headed to Iraq. He watched crates of supplies being loaded onto a C-17 at the base, which ships thousands of tons of cargo to front-line troops.

Bush was to give his speech to military personnel clad in camouflage. First, they dined with him after he filled his plate with beef brisket, beans and fruit.

Al-Qaida, led by Osama bin Laden, orchestrated the terrorist strikes on the United States by turning hijacked airplanes into killing machines. That was almost six years ago.

Now a fresh intelligence estimate warns that the United States is in a heightened threat environment, mainly from al-Qaida. The terror group is seizing upon its affiliate, al-Qaida in Iraq, to recruit members and organize attacks, the report found.

Bush sees such linkage as grounds for sticking with the fight in Iraq.

Yet his critics argue just the opposite point -- that the war is not reducing the threat to America, but increasing it by swelling and unifying al-Qaida's numbers.

Al-Qaida had no active cells in Iraq when the US invaded in March 2003, and its operation there is much larger now than before the war, US intelligence officers say.

The White House emphasizes that al-Qaida leaders in Iraq have sworn allegiance to bin Laden, who has avoided capture. He is believed to be living in the rugged Pakistan terrain.

In broad strokes, Bush's approach links the Iraq war to an event that Americans remember deeply -- the September 11 attacks -- as not the sectarian strife among Iraqis. That violent infighting among Iraqis has caused much of the United States to see little point in the US mission.