U.S. military engineers have reported that they shut down a pipeline used for illegal oil shipments from Iraq to Syria, Defense Secretary Donald H. Rumsfeld said Tuesday.

But Rumsfeld said he could not guarantee that the pipeline was completely shut off or that oil was not being clandestinely shipped from Iraq to Syria.

"We do not have perfect knowledge," Rumsfeld said at a Pentagon news conference. "We do know that they were instructed to shut it down and they have told us that they have."

Rumsfeld and Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said coalition forces had not destroyed any pipelines.

"They would not destroy the pipeline or any of the other infrastructure," Myers said.

The pipeline opened in 2000 and was believed to have handled about $1.2 billion worth of oil a year shipped in violation of the United Nations sanctions against Iraq.

Earlier, President Bush said victory in Iraq was "certain but it is not complete." Rumsfeld said "only a few" Iraqi cities remain contested, and troops were now doubling back to deal with remaining Iraqi fighters in smaller cities and towns they had bypassed earlier.

The future U.S. military role in the region was still being considered, Rumsfeld said. Saddam's hometown of Tikrit-- the last stronghold -- fell on Monday, and war planners are now restructuring and enlarging the American force that will focus more on providing humanitarian aid and looking for weapons of mass destruction.

In a separate appearance, Secretary of State Colin Powell looked ahead to postwar reconstruction.

"As one phase of this operation begins to wind down, another phase begins," Powell said.

The United States is involved in "a very active effort" to get other countries to contribute military forces for a postwar stabilization process, Rumsfeld said.

As for Iraq's ousted leaders, some of whom may be seeking haven in Syria, Rumsfeld said they will eventually be captured.

"I think there is no question there are going to be some people who are going to escape from that country. It's got porous borders," Rumsfeld said. "Obviously, the people in Iraq that ran that government are on our list. We'd like to have 'em. ... We'll even get most of them over time."

In Iraq, the first post-Saddam meeting of the nation's religious and political groups was meeting under U.S. auspices. While some small, sharp battles will continue to flare, Maj. Gen. Stanley McChrystal, vice director of the Pentagon's Joint Staff, said Monday, "The major combat operations are over."

Top officers have decided not to send the Army's 1st Cavalry Division into Iraq, a senior defense official said Monday. The 1st Armored Division still is set to go to Iraq but without its artillery, the official said.

The Army's 4th Infantry Division, which has some of the Army's newest equipment, is moving into Iraq from Kuwait. Its destination is northern Iraq, probably no farther north than the city of Kirkuk, where Kurdish forces ignored American requests and took the city last week, another senior military official said.

Two of the five Navy aircraft carrier battle groups engaged in the war are heading home this week. Each has about 80 planes aboard, including about 50 attack planes.

The Air Force has sent home the four B-2 stealth bombers that flew wartime missions, as well as F-117A stealth fighter-bombers and F-15C fighters, officials said.

With little public notice, the last two American aircraft based at Incirlik, Turkey, flew home Saturday to Shaw Air Force Base, S.C., ending 12 years of enforcing a no-fly zone over northern Iraq.

At least two attack submarines also have returned from the war. They and a number of destroyers and cruisers launched more than 800 Tomahawk cruise missiles into Iraq from the Red Sea, the eastern Mediterranean Sea and the Persian Gulf. No Tomahawks have been launched for several days.

About 300,000 U.S. troops are in the region now, though that number will decrease as the carriers leave. About 140,000 coalition soldiers are in Iraq, and that number is expected to rise as more Army troops arrive to perform stability and humanitarian operations.

Although U.S. troops have uncovered several suspected chemical or biological weapons sites, tests have come back negative from some sites and other final test results are pending. A U.S. military team was investigating the discovery Monday by Army troops of 11 buried shipping containers filled with laboratory equipment and 1,000 pounds of Iraqi documents.

U.S. forces haven't yet found any evidence linking Saddam's regime with Al Qaeda, a senior defense official said. He said it was unknown whether any Al Qaeda terrorists had been captured in Iraq.

The Pentagon said Monday the number of Americans killed in the war stood at 118, and four are missing in action.