By Matt Spetalnick

SYDNEY, Sept 8 (Reuters) - U.S. President George W. Bush will address a war-weary American public next week to "lay out a vision" for the U.S. role in Iraq as he tries to sell his strategy in the wake of a crucial report to Congress.

Heading home from an overseas trip on the eve of a political showdown over the unpopular war, Bush used his Saturday radio address to appeal for patience from Democratic lawmakers demanding a timetable for troop withdrawal.

Bush is under mounting pressure to change course in Iraq as top commander David Petraeus and Ambassador Ryan Crocker prepare to testify about a troop buildup the president says is making progress but which critics call a failure.

"I urge the members of Congress to listen to these two well-respected professionals -- before jumping to any conclusions," he said.

Fresh from a surprise visit to Iraq, Bush announced he would make his case in a televised address after Petraeus and Crocker deliver much-anticipated assessments starting Monday. CNN said the president would speak in prime time on Thursday.

"Next week," he said, "I will speak directly to the nation about the recommendations General Petraeus and Ambassador Crocker have presented to me.

"I will discuss the changes our strategy has brought to Iraq. I will lay out a vision for future involvement in Iraq -- one that I believe the American people and their elected leaders of both parties can support."

With his approval ratings near historic lows, largely due to anti-war sentiment, Bush has raised the prospect of a limited troop drawdown if security trends continue.

But he is unlikely to unveil a major shift in strategy any time soon in a war that has dragged on for more than four years, claiming the lives of more than 3,700 U.S. troops and tens of thousands of Iraqis.

WAR DEBATE

The Petraeus-Crocker report will fuel debate on Capitol Hill as lawmakers weigh whether to approve more funding for the war and as Democrats and a few Republicans insist that Washington should start bringing some of troops home.

The New York Times reported on Thursday that Petraeus told Bush he wanted to maintain heightened troop levels in Iraq well into next year but could accept a modest withdrawal of about 4,000 troops starting in January.

Petraeus's testimony, the centerpiece of the administration's mandated report to Congress, follows bleak independent assessments that Prime Minister Nuri al-Maliki has done little to achieve national reconciliation needed to curb sectarian violence.

Petraeus conceded in a letter to troops on Friday that the Shi'ite-dominated government's record on political reforms had been disappointing.

The Bush administration boosted troop levels -- now at 168,000 -- as part of a plan to improve security and give Iraqi politicians time to start bridging the sectarian divide.

Drawing upon his trip to Iraq's restive Anbar province on Monday, Bush reiterated, however, that he had seen promising gains on the ground, with Sunni tribal chiefs joining with U.S. forces against al Qaeda militants.

Bush left an Asia-Pacific summit in Sydney before it ended on Saturday to head home for final consultations on the Iraq report. He was due to stop briefly in Honolulu to review war strategy with commanders.

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