WASHINGTON  General David H. Petraeus, the commander of American forces in Iraq, and Ryan C. Crocker, the American Ambassador to Iraq, faced a new round of deep congressional skepticism today, not only about progress in the war and the prospects for eventual withdrawal, but also about whether the nation’s involvement in Iraq had made it more vulnerable on other fronts.

The general and the ambassador carried their message of “fragile and reversible” progress in the war to the House Armed Services Committee on Wednesday morning and the House Foreign Affairs Committee in the afternoon, the day after they testified before the corresponding committees in the Senate. Repeating the opening statements they made to the Senate panels, the two men once again yielded little fresh information about when the American military presence in Iraq could be reduced beyond the roughly 140,000 troops who will be left when the “surge” of about 30,000 extra troops sent to the country in 2007 winds down again in July.

Representative Ike Skelton, Democrat of Missouri and the chairman of the Armed Services committee, said in opening the first hearing on Wednesday that he saw far too few signs of real progress in Iraq, and warned that the continuing war’s strains on the American military were diverting the country from attending to other threats, starting with what intelligence reports say is a terrorist resurgence along the Afghanistan-Pakistan border. “The effort in Iraq is putting at risk our ability to decisively defeat those most likely to attack us,” he said.

Mr. Skelton said that while the “surge” had temporarily lowered the amount of violence in Iraq, Iraqis had failed to “step up” to take advantage of the improved security. And he said he feared that officials in Baghdad would feel no sense of urgency to pursue sectarian reconciliation and achieve full autonomy until “we take the training wheels off and let the Iraqis begin to stand on their own two feet.”