Updated

Announcing a plan for rapid troop withdrawals in Iraq would signal Iraqis to start "building the walls, stocking ammunition and getting ready for a big nasty street fight" rather than working toward reconciliation, the U.S. ambassador to Iraq said Tuesday.

Amb. Ryan Crocker told senators that he recognizes times are tough in Iraq, and lawmakers want to draw down the number of U.S. forces in Iraq from its current peak of 168,000, but any rapid redeployment could topple the shaky progress that has been made as a result of the recent surge.

"An Iraq that falls into chaos or civil war will mean massive human suffering — well beyond what has already occurred within Iraq's borders," Crocker said

Crocker and Gen. David Petraeus, the head of Multinational Forces In Iraq, were testifying for a second day on Capitol Hill on military and political progress in Iraq. They faced lawmakers on both sides of the aisle who are under pressure to bring troops home.

President Bush will accept Petraeus and Crocker's recommendations — which was expected — and will call for troop reductions of 30,000 by summer 2008, a senior administration official told FOX on Tuesday. Bush will be following up on this week's testimony with a national address of some sort later this week.

Tuesday, Petraeus said the total number of troops to be withdrawn by next summer will return troop levels to its pre-surge numbers of 130,000. Sending home one Marine expeditionary unit, two Marine battalions and five Army brigades would allow the remaining forces to continue operational and strategic considerations, including fighting off Al Qaeda in Iraq and Iranian "militia extremists."

Republican Sen. Norm Coleman, facing a tough re-election in Minnesota next year, said he appreciates plans announced by Petraeus, but Americans are looking for a longer-term vision than a return by the leaders in six months to deliver another assessment.

"Americans want to see light at the end of the tunnel," said Coleman.

"We should not be asking any more American troops to sacrifice their lives and limbs for Iraqi politicians who refuse to compromise. That's why I believe more strongly than ever that we need to change course in Iraq," added Sen. John Kerry, D-Mass.

Other senators asked whether Iraqis even care about the purpose behind the American sacrifice.

"At our last hearing on Iraq, featuring the GAO report on benchmarks, I expressed skepticism that the success or failure of the benchmarks will be determinative in Iraq. Benchmarks are an important starting point for debate, but they do not answer many questions, including the most fundamental question pertaining to Iraq, namely: Do Iraqis want to be Iraqis?" asked Sen. Richard Lugar, R-Ind., the ranking member of the Senate Foreign Relations Committee.

"From my perspective, the most important questions we have to ask are these: Are we any closer to a lasting political settlement in Iraq at the national level today than we were when the surge began eight months ago? And if we continue to surge for another six months, is there any evidence that the Sunnis, the Shias and the Kurds will stop killing each other and start governing together?" asked Sen. Joe Biden, D-Del., the panel's chairman.

"In my judgment, I must tell you, based on my experience and my observation here, as well as in-country, the answer to both those questions is no," said Biden, a 2008 presidential candidate.

But in an afternoon session with the Senate Armed Services Committee, Republican presidential candidate John McCain stood firm in his support for seeing out the mission.

"It's the only approach that has resulted in real security improvements in Iraq," McCain said, warning his colleagues against continued efforts to set a date for withdrawal.

"As Ambassador Crocker has noted, no one can be certain of success. We can be sure, however, that should the United States Congress succeed in legislating a date for withdrawal, and thus surrender, then we will fail for certain. ... Make no mistake, the consequences of American defeat in Iraq will be terrible and long-lasting."

At the White House, spokesman Tony Snow wouldn't say whether President Bush will start withdrawing additional troops he sent to Iraq but hold off on deciding further reductions until at least March — as Petraeus recommends. Bush is expected to address the nation on the matter this week.

Snow, though, said that Bush's thinking has not changed: success in Iraq is vital to U.S. security, regardless of public opposition to the war. "If some of the steps he takes make him unpopular, he will accept that hit," Snow said.

Crocker told lawmakers that no single point in time will be the mark with which to measure U.S. victory in Iraq. Instead, victory will be something determined in the future.

"There will be no single moment at which we can claim victory. Any turning point will likely only be recognized in retrospect. This is a sober assessment, but it should not be a disheartening one," Crocker said, adding that after the fall of Saddam Hussein, "a new Iraq had to be built almost literally from scratch."

Since then and despite efforts by Al Qaeda and insurgents to destroy U.S. efforts to rebuild Iraq, much progress has been made in crafting institutional frameworks where none previously stood.

Petraeus said a lot of the progress since the surge is due in part to the tribes and sheiks in different regions agreeing to work with the U.S. forces and throw off Al Qaeda.

"In a number of cases, the progress is not just because of more forces sitting on a problem; it's the result of a fundamental change on the ground. Nowhere is that more visible, obviously, than Anbar province where — and this bears out the whole idea that it is about political change," Petraeus told senators. "What happened in Anbar is politics. It was the result of tribes, sheikhs saying no more to Al Qaeda. That's a political decision, to oppose an organization with which they were, at least tacitly, in league, and, perhaps, supporting."

The leaders were in town for two days to deliver a congressionally mandated report on 18 Iraqi benchmarks laid out by Congress early this year. Several reports have shown what war opponents have been bemoaning for weeks — that the benchmarks have been met only partially, and the military and security achievements have not yielded political reconciliation.

"Rather than identifying the very limited tactical gains that have been made at great cost and using them to justify the maintenance of a failing strategy, I believe it is time to change course," said Sen. Barack Obama, D-Ill., a 2008 presidential candidate. "Over 3,700 American servicemen and women have died in this war and over 27,000 have been seriously wounded. Each month, this misguided war costs us a staggering $10 billion, and when all is said and done, this will have cost us $1 trillion. ... The time to end the surge and to start bringing our troops home is now — not six months from now."

"Are we going to continue to invest American blood and treasure at the same rate we're doing now, for what? The president said, 'Let's buy time.' Buy time? For what? Every report I've seen, and I assume both of you agree with this, there's been really very little, if any, political process. That is the ultimate core issue, the political reconciliation in Iraq," said Sen. Chuck Hagel, R-Neb.

Crocker acknowledged that Iraq has been enormously dysfunctional but said a clear linkage has been made between "security conditions, levels of violence and the capacity of people in an environment to move meaningfully toward reconciliation." Those preconditions had not existed until now, he said.

"Iraq in my judgment almost completely unraveled in 2006 and the very beginning of 2007. A sectarian violence beginning in February '06 just spiraled up. Under those conditions, it's extremely difficult, it is impossible to proceed with effective governance or an effective process of national reconciliation. It is just in the last couple of months that those levels of violence have come down in a measurable way," Crocker said.

"A moderately encouraging factor is that when security does improve, as we saw in Anbar, political life starts up again. For example, in Anbar now, every significant town has a municipal council, has an elected mayor. ... So that suggests to me that, at a minimum now, we've got an environment developing, not fully developed, but developing with violence at low enough levels where a meaningful discussion on national reconciliation can take place," Crocker said.

"We are talking about really, sort of, finding who are the irreconcilables and trying to isolate them and then to help the Iraqi government to bring the reconcilables to become part of the solution instead of part of the problem. And that is what has happened, again, most notably in Anbar but it is applicable to some degree in other areas, as well," Petraeus added.

Tuesday's testimony — falling on the sixth anniversary of the Sept. 11, 2001, terror attacks — followed an exclusive hour-long appearance with FOX News in which the top military and diplomatic leaders said a quick departure is not the best course for the region or the U.S. Al Qaeda in Iraq would regain its faltering foothold, and a premature withdrawal would leave instability in many areas that are now achieving sustainable security.

On the diplomatic track, Crocker added that he's trying to convince his Iranian counterpart — who is a member of the elite Quds military force that controls Iranian foreign policy — that it's not in Iran's interest to try to destabilize Iraq.

"I think you see a collision in Iran between their long- term strategic interests and their narrow tactical desires. Their narrow tactical desires I would define as trying to administer a defeat to the U.S. in Iraq. The problem they've got is that, if they are able to create circumstances that cause us to reconsider our commitment, the result is going to be a chaotic Iraq that, over the long run, could potentially be dangerous for them, as well," Crocker said.