General Petraeus warned that gains from the so-called surge were "fragile and reversible" and recommended that the "drawdown" of US forces continued, before a 45 day period of "consolidation and evaluation" is taken. Spike in violence
The US military is currently withdrawing five combat brigades that were sent to Iraq for the "surge" early last year, a process to be completed by July.
This would bring troop levels down from about 158,000 to 140,000.
A recent spike in violence in Iraq involving clashes between Iraq security forces and Shia militas has left hundreds of people dead and thrust Iraq back to the forefront of campaigns for the US presidential election in November.
The White House and members of the Republican party say the "surge" successfully lessened violence and argue a pause in troop withdrawals to pre-surge levels provides the means to assess the results of the "surge".
John McCain, the presumptive Republican candidate, told the Senate Armed Services committee ahead of Petraeus's testimony on Tuesday that "much needed to be done but said it was possible to "talk with real hope and optimism about the future of Iraq and the outcome of our efforts there.'' Democrat criticism
However, earlier several Democrats criticised Petraeus' plan to halt withdrawals, saying the surge has not yielded sufficient political progress in Iraq and no end to the conflict is foreseeable.
"The height of irresponsibility was going in," Democratic presidential hopeful Barack Obama told NBC news on Tuesday.
"It compounds the irresponsibility if all we're doing is simply moving the goal posts."
His Democratic rival, Hillary Clinton, also criticised the White House for not doing more to end sectarian strife in Iraq.
"Clearly, the surge hasn't worked. The point of the surge, it's stated rationale, has not been fulfilled," she told ABC news.