AL-ASAD AIR BASE, Iraq (AP) – President Bush made a surprise visit to Iraq today, using the war zone as a backdrop to argue his case that the buildup of American troops is helping stabilizing the nation.

The president secretly flew 11 hours to Iraq as a showdown nears with Congress over whether his decision in January to order 30,000 more American troops to Iraq is working. He landed at an air base in Anbar province west of Baghdad.

Next week, General David Petraeus, the top American commander in Iraq, and Ryan Crocker, the American ambassador in Baghdad, testify before Congress. Their assessment of the conflict, along with a progress report the White House must give lawmakers by Sept. 15, will determine the next chapter of the war.

America cannot sustain the troop buildup indefinitely. And with Democrats calling for withdrawals and a rising American death toll that has topped 3,700, the president is hardpressed to give Iraqi Prime Minister al-Maliki’s much more time to find a political solution to the fighting.

Mr. Bush stopped in Iraq ahead of his visit to Australia for an economic summit with Asia-Pacific leaders. The trip was a closely held secret for obvious security reasons, although speculation about the trip arose late last month when first lady Laura Bush said she was staying home to tend to a pinched nerve in her neck.

The president, who also went to Iraq at Thanksgiving 2003 and in June 2006, was scheduled to leave for Australia on Monday, but Air Force One took off from Andrews Air Force Base Sunday evening instead.

He was joined by his top advisers, including National Security Adviser Stephen Hadley. Secretary of Defense Gates was traveling there separately. The mission to shore up support for the war was shared with only a small circle of White House staffers and members of the media, who were told that if news of his trip leaked early, it would be scrapped.

The White House arranged Bush’s trip at a pivotal juncture in the Iraq debate. Some prominent GOP lawmakers have broken with Bush on his war strategy, but so far, most Republicans have stood with Mr. Bush. In exchange for their loyalty, they want to see substantial progress in Iraq soon.

Making his case before the Sept. 15 report deadline, Mr. Bush recently delivered a series of speeches to highlight how the temporary military buildup has routed out insurgents and foreign fighters.

The president has described what he calls “bottom-up” progress in Iraq and often cites a drop in violence in Anbar Province, once a hotbed of insurgency.

The turnaround occurred when Sunni Arab leaders joined forces with Americasn troops to hunt down members of Al Qaeda, although it’s unclear whether they’ll back a unified Iraqi government as well.

Critics of the war argue that while the troop buildup may have tamped down violence, the Iraqis are making almost no headway toward political reconciliation. They cite a handful of gloomy progress reports trickling out of Washington that show some success in curbing violence, but little progress toward political power-sharing agreements.

There are now 162,000 American troops in Iraq, including 30,000 that arrived since February as part of Mr. Bush’s revised strategy to provide security so Iraqi leaders could build a unity government.

Mr. Bush met on Friday with his top military chiefs at the Pentagon who expressed concern about a growing strain on American troops and their families from long and often multiple combat tours.

Still, early indications are that the president intends to stick with his current approach – at least into 2008 – despite pressure from the Democratic-led Congress and some prominent Republicans. Right now, the White House is working to keep Republican members of Congress in the president’s fold to prevent Democrats from amassing the strength to slash war funds or mandate immediate troop withdrawals.