WASHINGTON (AFP) -- Iraq war commander General David Petraeus is poised to mount a staunch defense of the U.S. troop surge strategy today, in one of the most dramatic appearances of a witness before Congress in years.

The talismanic general faces a hostile barrage from Democrats over if and when troops can come home from a four-year war that has killed more than 3,700 U.S. soldiers, tens of thousands of Iraqis and cost half a trillion dollars.
Joined by U.S. ambassador to Baghdad Ryan Crocker, Petraeus will swap Baghdad's stifling heat for cool congressional committee rooms today and tomorrow, to compliment a report on the war which President George W. Bush must deliver by September 15.
He will argue the contentious strategy to surge 28,500 extra troops into war-battered Iraq announced in January, has slashed sectarian violence and should be extended.
But he also is expected to accept gradual cuts in the 168,000 strong U.S. garrison in Iraq, beginning early next year -- though the reductions he has in mind will likely not satisfy anti-war Democrats.
------------Tactical momentum
""My sense is that we have achieved tactical momentum and wrested the initiative from our enemies in a number of areas of Iraq,"" Petraeus wrote in a letter to U.S. forces.
But he admitted political reconciliation in Baghdad had not ""worked out as we had hoped"" though he was optimistic ""a stable and secure Iraq"" was possible.
Democrats have for months seen Petraeus's testimony as a landmark moment in the war, and hoped to use it to fracture Republican support for Bush.
But they appear to have been outflanked by the White House during August, and the threat of a Republican revolt seems to have faded.
Democrats will claim sacrifices made by U.S. soldiers were in vain, with no sign the Iraqi government has made progress the surge was designed to promote.
Petraeus's expected contention that sectarian violence is receding in Iraq will also be under fire, after a U.S. official auditor Friday cast doubt on the figures.
Democrats are under pressure from grass roots supporters who helped them capture Congress last year, but slim majorities and Bush's constitutional powers have thwarted their anti-war drive.
Rahm Emanuel, chairman of the House of Representatives Democratic caucus, accused the administration of ""cherry-picking"" progress in Iraq.
""We don't need a report that wins the Nobel Prize for creative statistics or the Pulitzer for fiction,"" Emanuel said.
The stage was set for Petraeus by two reports examined in high-stakes congressional hearings last week.
In one, the Government Accountability Office concluded Iraq had failed to meet 11 of 18 benchmarks for political reform.
In a second study, retired marine general James Jones warned U.S.-trained Iraqi forces would not be able to assume combat duties alone for 12 to 18 months.
Faced with such realities, not only Democrats have political concerns -- with congressional elections looming in 2008, Republicans fear having to woo voters while again defending an unpopular war.
-----------Chasms in politics
Petraeus's testimony will expose chasms in U.S. politics forged by the war.
""We can continue to support the new strategy and the real progress ... in Iraq,"" said Republican Senator John McCain and 2008 Republican presidential candidate Friday.
""Or we can choose the path of surrender.""
Democratic feeling is just as intense.
Tom Lantos, chairman of the House Foreign Affairs committee, which welcomes Petraeus and Crocker in their first hearing in a joint session with the House Armed Services committee Monday, has already dismissed Bush's impending report.
He branded the survey ""a political document -- drafted in Washington by those who see Iraq not as it is, but as they would like it to be.""
McCain is not the only presidential candidate eyeing an opening.
Pacesetting Democrat Hillary Clinton, who has pledged to start troop withdrawals if she is elected, will likely confront Petraeus in the Senate Armed Services committee on Tuesday.
Her chief rival Barack Obama is a member of the Senate Foreign Relations committee, which welcomes the General the same day.
Republican presidential candidates, who have largely supported the unpopular surge, will be hoping Petraeus can buy them some time in Iraq, before first nominating contests early next year.