WASHINGTON — The top U.S. commander in Iraq called Tuesday for halting U.S. troop withdrawals indefinitely this summer to assess security gains and said future reductions should be based on conditions and not timetables.

During a highly anticipated appearance before a key Senate panel, Army Gen. David Petraeus, flanked by the U.S. ambassador in Iraq, Ryan Crocker, called for a 45-day "period of consolidation and evaluation" once the troop levels have been brought down to about 140,000 or so in July.

"At the end of that period, we will commence a process of assessment to examine the conditions on the ground," Petraeus said in his determined military cadence. "This process will be continuous, with recommendations for further reductions made as conditions permit."

He would not commit to any troop levels after that.

"This approach does not allow (the) establishment of a set withdrawal timetable," Petraeus said. "However, it does provide the flexibility those of us on the ground need to preserve the still-fragile security gains."

Petraeus painted probably the clearest picture to date of what the U.S. presence in Iraq will look like for the foreseeable future, if not the remainder of the Bush presidency. Bush, who has voiced great confidence in Petraeus, is expected to take his advice.

One of the leading war critics on Capitol Hill, Sen. Carl Levin, D-Mich., was clearly disappointed with Petraeus' recommendation. The chairman of the Armed Services Committee has long argued that U.S. forces are a crutch for the Iraqis.

"I think this open-ended pause takes the pressure off the Iraqi leaders to take responsibility for their own country," he said.

The report by Petraeus and Crocker comes as violence in Iraq has spiked, raising questions about the success of the troop surge President Bush started more than a year ago and has touted as a success.

Even as Petraeus and Crocker delivered their report to lawmakers, 11 U.S. troops died in 48 hours of fighting in Iraq. Altogether, the war has claimed the lives of more than 4,000 U.S. troops and cost taxpayers about $500 billion.

Petraeus said the recent spike in fighting was an anomaly and that overall violence has come down considerably under the surge. But security is still fragile, he said.

"The military surge has achieved progress, but that progress is reversible," he said.

The Iraqis have recruited more than 400,000 army and security troops. In the recent flare-up of violence in the port town of Basra, Petraeus said Iraqi forces took the lead, although the outcome of the fighting was inconclusive.

Crocker told senators that Iraq is making some of the political progress, such as the scheduling of provincial elections, that it must in order to bolster the conditions necessary for an eventual U.S. withdrawal. But he acknowledged it has been slow, hard work.

"Looking ahead, mister chairman almost everything about Iraq is hard," he said. "But hard does not mean hopeless. ... Our current course is hard, but it's working. ... We need to stay with it."

Congress will be debating that issue when it considers Iraq war funding later this month, and the testimony by Petraeus and Crocker is likely to weigh heavily in that.

Their first congressional report in September — where they convincingly argued the surge was working — changed the dialogue on Iraq and put war opponents on their heels.

They were able to keep much of the focus on the short-term tactical successes of the operation such as the reduction in violence. That, in turn, laid the groundwork for arguments that politicians shouldn't interfere with it.

Tuesday's appearance by the general and ambassador also set the stage for some political theater. All three presidential candidates — Sen. John McCain, R-Ariz., Sen. Hillary Rodham Clinton, D-N.Y., and Sen. Barack Obama, D-Ill — sit on the Senate committees that are holding hearings.

McCain, whose seniority permitted him to speak early, reiterated his strong backing of the troop surge and warned his fellow lawmakers about the dangers of undoing its gains.

"By giving our men and women in uniform the time and support necessary to succeed in Iraq, we have before us a hard road," McCain said. "The Congress must not choose to lose in Iraq. We should choose instead to succeed."

War critics pressed Crocker on Iraq's financial situation. Iraq has an estimated $40 billion in reserves in Swiss and American banks, and yet Americans continue to dump huge sums into Iraq's reconstruction.

"We need to find a way for Iraq to fund more of its own present and future," said Sen. Ben Nelson, D-Neb. "It doesn't make sense for us to be financier of first resort."

Crocker said Iraq's economy is making strides and warned against cutting off important development projects before they've borne fruit.

While Petraeus and Crocker were cautiously optimistic on most points, they warned lawmakers of the continuing problems posed by neighboring Iran, which they said remains a serious military and political force in southern Iraq.

"Iran has said publicly it will fill any vacuum in Iraq," Crocker said.

Contact John Yaukey at jyaukey@gns.gannett.com.