Secretary of Defense Donald Rumsfeld said Thursday the U.S. probably won't find the chemical and biological weapons it believes are hidden in Iraq unless the Iraqis show American forces where they are.

"I don't think we'll discover anything, myself," Rumsfeld said at a town hall-style meeting with Pentagon employees. "I think what will happen is we'll discover people who will tell us where to go find it. It is not like a treasure hunt where you just run around looking everywhere, hoping you find something."

Sweeping the country clean of such weapons was one of the primary reasons President Bush gave for invading Iraq March 20 and dethroning dictator Saddam Hussein. To date, U.S. troops have come across suspicious devices, chemicals and facilities, but all tests on them have come out negative or inconclusive.

A Defense Department employee asked Rumsfeld what could be done to prevent accusations that the U.S. planted any chemical or biological weapons discovered. Rumsfeld said he believed such charges are likely and there is little the United States can do to avoid it.

Only in the past few days, Rumsfeld said, have enough weapons searchers arrived in parts of Iraq where U.S. intelligence indicates chemical or biological weapons could be found.

"The teams have been trained in chain of control, really like a crime scene," he said. "That will not stop certain countries and certain types of people from claiming, inaccurately, that it was planted."

Appearing with Rumsfeld was Gen. Richard Myers, chairman of the Joint Chief of Staff, who cautioned against thinking that the fall from power of Saddam's Baath Party rule means the war is over.

"I wish I could say that we're winding all this down, but I can't," Myers said.

Rumsfeld made a similar point.

"The war is not over," he said. "We know that. There are still pockets of resistance, shots are still being fired and people will still be killed. And as we gather here people are still fighting in Iraq and elsewhere."

As the hunt for WMD continues, coalition forces are also scouring Iraq for its top leaders, and U.S. officials have told Fox News that the hunt has intensified Friday, as they feel several of the "top 55 Iraqi regime leaders" are now in located in northwest Iraq. Officials feel these leaders are hiding west of Mosul, and are trying to cross the border into Syria.

Special Operations teams have been investigating local tips to try to find out where these leaders may be. Even as coaltion troops continue to attempt to seal the Syrian border, officials say that the area is "extremely porous" and there are a lot of routes into Syria.

Despite the intensified hunt for Iraq's leaders, the crucial air campaign that helped unravel Iraq's defenses is all but over.

As a result, more of the air power used against Iraq is leaving the region.

A second Navy aircraft carrier departed the Persian Gulf on Thursday, leaving only the USS Nimitz battle group on station in the Gulf, defense officials. Both the Navy and the Air Force are bringing aircraft home to allow pilots and crews a respite after one of the most intense air campaigns in history.

The USS Constellation, on its final overseas mission before going into a scheduled retirement, left the Gulf Thursday, one day after the carrier USS Kitty Hawk departed for its homeport in Yokosuka, Japan, said the officials, speaking on condition of anonymity.

Two other carriers that participated in the air war from positions in the eastern Mediterranean -- the USS Harry S. Truman and the USS Theodore Roosevelt -- are going to alternate on port visits in the Mediterranean but not head home yet, the officials said.

The USS Carl Vinson, which took the Kitty Hawk's place in the Pacific in February, is making a port call in Guam but is to return to the vicinity of Japan and remain while the Kitty Hawk is repaired in a Japanese shipyard, officials said.

The Pentagon said the U.S. death toll from the war in Iraq rose by one to 126. Marine Cpl. Jason David Mileo, 20 of Centreville, Md., was shot and killed Monday after being mistaken for an Iraqi soldier, it said. He was in the Baghdad area, assigned to the 3rd Battalion, 4th Marine Regiment, 1st Marine Division, whose headquarters is at Twentynine Palms, Calif. The matter is under investigation.

Three American service members are listed as missing -- one Army soldier and two Air Force pilots.

In addition to those killed, 495 Americans have been wounded in action, according to the Pentagon.

"Some are going to recover very quickly; others are going to have to live with their injuries for the rest of their lives," Myers said. "They'll never escape the pain in some cases or, perhaps, regain lost opportunities this conflict has brought upon them."

The Associated Press contributed to this report.