The assessment by Gen. David Petraeus could be a turning point in the conflict and is considered vital to any decisions by President George W. Bush on force levels as he faces demands from Democrats and some senior Republicans for U.S. troops to start leaving Iraq.
A U.S. official who asked not to be named said on Sunday that Petraeus and U.S. Ambassador to Iraq Ryan Crocker will argue that a major pullout of U.S. forces would hurt progress made since troop numbers were increased by 30,000 earlier this year.
They speak before a joint session of the House Armed Services and Foreign Relations committees. Petraeus' testimony starts at 12:30 p.m./1630 GMT.
Citing U.S. officials, The New York Times reported on Monday Petraeus has recommended that decisions on major troop cuts in Iraq be delayed until March 2008.
A majority of Americans are skeptical of what Petraeus will report and most support setting a timetable to withdraw forces regardless of what is going on in Iraq, according to a USA Today/Gallup poll conducted released on Monday.
Some Democrats are worried Petraeus will seek more time for progress in Iraq and avoid giving definitive answers.
Now, it looks like General Petraeus is going to ask for six more months. And it's clear that this administration is trying to delay the ultimate judgment until the next president gets into office, Sen. Edward Kennedy, a Massachusetts Democrat, said on Sunday on CBS.
In testimony this week, Petraeus is due to assess whether Bush's move to add 30,000 troops in Iraq this year has succeeded -- and what troop levels are needed going forward.
The conventional wisdom in Washington, driven home by a fusillade of recent official reports, is that the increase in U.S. troops may have created some tactical military gains -- especially in Baghdad and Anbar province -- but that political reconciliation between Iraq's various ethnic groups is stalled.
PRESSURE TO DECREASE TROOPS
Bush is under mounting pressure to pull out at least some of the 168,000 forces in Iraq after more than four years of war, in which over 3,700 U.S. troops and tens of thousands of Iraqis have died. He raised the prospect of a drawdown on a recent visit to Iraq, but said any withdrawals had to come from a position of strength.
The president makes a prime-time speech on Thursday on his future strategy in Iraq, and is to submit his own assessment to Congress by Sept 15.
Pentagon officials acknowledge the 30,000 troop increase faces a time limit because of rotation schedules. Some Republican war supporters suggest that waiting a few months before withdrawing may be the best strategy, especially to avoid a wider Middle East conflagration involving Iraq's neighbors Syria and Iran.
I think we're at a point where you could, in some months from now, start redeploying and withdrawing troops, if you give it (the surge) a chance to succeed, said Sen. John McCain, a presidential hopeful, on Sunday on ABC's This Week.
Many Democrats have made it clear that come what may in the Petraeus and Crocker reports, they want U.S. troops out of Iraq.
Pointing to continuing violence and political stalemate, they are not prepared to believe tales of success.
The truth of the matter is that the American administration's policy and the surge are a failure, Delaware Sen. Joe Biden, chairman of the Senate Foreign Relations Committee and a Democratic presidential candidate who just returned from Iraq, said on NBC's Meet the Press.