WASHINGTON (CNN) -- Defending the "surge" of U.S. troops in Iraq and insisting that a stable and democratic society there was still within reach, the top two U.S. officials in the war zone ended their second contentious day of testimony on Capitol Hill Tuesday.
Gen. David Petraeus, left, and Ambassador Ryan Crocker observe a moment of silence for the victims of 9/11.
In a Senate Foreign Relations Committee hearing, senators pressed Ambassador Ryan Crocker and Gen. David Petraeus for a measurable sign of success that would enable a pullout of U.S. troops from Iraq to begin.
Petraeus said he "would be very hard-pressed to recommend" continuing the so-called troop surge beyond March if conditions in Iraq had not changed from what they are now.
But he told lawmakers that Iraqi security forces are improving and are able to "shoulder more of the load, albeit slowly" amid continuing concerns about sectarian elements within their ranks.
"Overall, our tactical commanders see improvement in the security environment," Petraeus said, repeating assertions about the decline of violence during the surge.
In the surge, President Bush ordered nearly 30,000 additional troops to Iraq in January as part of a campaign to pacify Baghdad and its surrounding provinces.
At one point Tuesday, Sen. John Warner, R-Virginia -- an outspoken critic of the state of affairs in Iraq -- asked Petraeus if the strategy he was laying out before Congress was making America safer.
"Sir, I believe that this is indeed the best course of action to achieve our objectives in Iraq," Petraeus answered.
"Does that make America safer?" Warner repeated.
"Sir, I don't know, actually. I haven't sat down and sorted it out in my own mind. What I have focused on and what I'm riveted on is how to accomplish the mission of the Multi-National Force-Iraq," Petraeus replied. Watch how Republicans challenged Petraeus »
But Sen. John McCain, R-Arizona, warned the consequences of American defeat in Iraq would be terrible and long-lasting.
"There is in some corners a belief that we can simply turn the page in Iraq, come home, and move on to other things. This is dangerously wrong. If we surrender in Iraq, we will be back," he said.
McCain then asked Petraeus to confirm reports that he said Iraq was the central front in the war on terror.
"Is that a correct quote?" McCain asked.
"That is correct, sir," Petraeus replied, saying his view was based on his conversations with the director of the CIA and other officials.
Crocker said he believes a "secure, stable and democratic Iraq" at peace with its neighbors is an attainable goal. He said dramatic security improvements in north and west Iraq "have opened the door for meaningful politics."
But this upbeat assessment and others were met with stinging criticism from some senators.
"I ask you to take off your rosy glasses," Sen. Barbara Boxer, D-California, said at one point during the hearing.
The questions and comments were so intense at times they prompted Sen. Mark Pryor, D-Arkansas, to ask whether the two men were ready to go back to Baghdad.
"Baghdad's never looked so good, Senator," Crocker answered to laughter.
Earlier, the diplomat said the Iraqi government is dysfunctional, but the "good news" is that Iraqis recognize that fact and are working to bridge sectarian divisions.
"Iraq, in my judgment, almost completely unraveled in 2006, and the very beginning of 2007, as sectarian violence after February '06 just spiraled up," Crocker said.
"It is just in the last couple of months that those levels of violence have come down in a measurable way," allowing political reconciliation, he said.
"Iraq is experiencing a revolution, not just regime change," Crocker said. "It is only by understanding this that we can appreciate what is happening in Iraq and what Iraqis have achieved as well as maintain a sense of realism about the challenges that remain."
Democrats on the committee were looking for a timetable for U.S. troops to come home.
"General, of what you know today, if the commander in chief said to you, 'Gen. Petraeus, how many more years do American soldiers have to continue in Iraq,' what would your answer to him be?" asked Sen. Robert Menendez, D-New Jersey.
"I cannot predict that," Petraeus replied.
"I'm as frustrated with the situation as anybody else," Petraeus continued in a testy exchange with Menendez. "This is going on three years for me, on top of a year deployment to Bosnia as well. So my family also knows something about sacrifice."
Tuesday's hearings were held on the sixth anniversary of the September 11, 2001, attacks, and Feingold raised the specter of that event.
He asked whether Pakistan or Iraq is more important to the fight against al Qaeda. Neither man would say.
Crocker responded to Feingold by saying, "In my view, fighting al Qaeda is what's important, whatever front they're on." But Feingold said their inability to provide an answer was indicative of the "myopia of Iraq."
As he did Monday in a House hearing, Petraeus said security forces have made progress that will permit the reduction of U.S. forces in the months ahead.
He said there have been improvements in sectarian relations in the Iraqi capital, but not to the point that the different factions can completely commingle.
Outside the ethnically and religiously mixed enclaves of southeastern Baghdad, it remains hazardous for a Sunni to travel into Shiite neighborhoods, Petraeus said.
In his opening statement, committee chairman Sen. Joseph Biden, D-Delaware, said he saw no evidence of sectarian amity when he was recently in Anbar province, which is west of Baghdad.
"If we killed or captured every jihadist in Iraq tomorrow, we would still face a major sectarian war that is pitting Iraqis' future against our interest," Biden said.
"The fact of the matter is that American lives remain in jeopardy, and, as I said, if every single jihadi in the world was killed tomorrow, we'd still have a major, major war on our hands."
On Monday, Petraeus and Crocker addressed a six-hour joint hearing of the House Armed Services and Foreign Relations committees. E-mail to a friend