BAGHDAD, Iraq — America’s chief military and civilian officials in Iraq sought to steady American public opinion yesterday by pledging that local security forces should be able to take full control of the country within 12 to 18 months.

Appearing together in Baghdad, Zalmay Khalilzad, America’s ambassador, and the American commander, General George Casey, said the Iraqi government had now accepted a timetable to restore order in the country.

The new “national compact” would lay out a series of benchmarks that, if achieved, would restore stability and allow coalition forces to withdraw within a “reasonable” time frame.

These would include disbanding militias, making changes to the constitution, and a new agreement on sharing the country’s oil wealth among its sectarian and ethnic groups.

With midterm elections to be held in America next month, polls show that voters consider Iraq to be the number one issue and only one in five believes the war is being won.

In a direct appeal to the American people, Mr. Khalilzad said the struggle to save Iraq was “the defining challenge of our era.”

“The recent sectarian bloodshed in Iraq causes many to question whether the United States can succeed,” he said. “[But] our goal has not changed. Despite the difficult challenges we face, success in Iraq is possible and can be achieved.”

General Casey continued the upbeat message. America had never lost a battle since the war began in 2003, he said, adding that the American military would succeed in Iraq but that it would need patience and resolve from the American public.

The White House, under intense pressure in the last weeks of a tight election campaign, has struggled to redefine the terms of the debate on Iraq.

President Bush’s spokesman, Tony Snow, signaled that Washington’s commitment to Iraq was being recalibrated. He said yesterday: “What you have is not ‘stay the course’ but a study in constant motion by the administration and by the Iraqi government and, frankly, also by the enemy.”

One of Washington’s leading political consultants, David Gergen, said the recent spiral of violence against American troops forced the Bush administration to review its strategy. “They’re scrambling,” he said. “They’re in a real mess in Iraq, and they know it, but they don’t admit it publicly.”

The announcement in Baghdad followed a series of leaks that indicated that a dramatic change of course could be announced. That did not transpire.

Nor was there any clue yesterday as to what would happen if the Iraqi authorities failed to meet the timetable.

However, the two American leaders unleashed a fierce attack on Iraq’s neighbors. “Both Iran and Syria continue to be decidedly unhelpful by providing support to the different extremists and terrorist groups operating inside Iraq,” General Casey said.

[American officials yesterday said moreAmerican troops might be needed to quell the bloodshed, the AP reported. American officials previously said they were satisfied with troop levels and had expected to make significant reductions by year’s end.]