Lt. Gen. John Abizaid (search), nominated by President Bush to oversee U.S. military operations in Iraq, told senators Wednesday that although he's confident weapons of mass destruction will be found in Iraq, he too is wondering why none have yet been found.

Meanwhile, Pentagon officials told Fox News that, "there are going to be a lot of people with egg on their face when we find this stuff … and we will."

Abizaid, nominated to replace Gen. Tommy Franks (search) as head of U.S. Central Command (search), also said the number of U.S. soldiers will likely be reduced from the current 145,000, but that "for the foreseeable future, we will require a large number of troops for Iraq."

Abizaid said U.S. forces and weapons experts are piecing together information, from documents and people, to find out what happened to the weapons between 1998 and today.

"I'm confident we'll show there was deception and I'm confident it will lead us to the actual weapons," he said.

Abizaid's confirmation hearing came as both the Senate Armed Services and Senate Intelligence committees have begun reviewing the accuracy of prewar intelligence on Iraq's weapons of mass destruction.

That intelligence served as the basis for the war, but has been called into question in the United States and abroad because no weapons have been found. Democrats, in particular, have been voicing vocal criticism of the administration for lack of more substantive evidence of such weapons.

Some critics have even charged that higher-ups like Vice President Dick Cheney and CIA Director George Tenet pushed to make sure the evidence was solid enough to convince Congress and the world.

Asked whether he believed weapons intelligence had been manipulated, Abizaid said: "I firmly believe there was no distortion of intelligence."

"I really believe that the intelligence communities did their best to give us their best judgment," he said. "That we didn't get it completely right is what I consider to be a fact. Will we figure out what we didn't know? I think we will."

Senior Defense officials on Wednesday confirmed to Fox News that some samples of possible chemical or biological materials have been sent out of Iraq to be tested in different independent labs. They also said some "precursor chemicals" have been found in Iraq.

One official described it as "a significant amount" in recent weeks. "Precursor chemicals" are the chemicals that can be mixed with other ingredients, including other chemicals, to produce chemical weapons.

Pentagon officials are still confident that coalition troops will discover the actual weapons but they are also building the case and gathering the evidence about Iraq's weapons program and how it was poised to "churn out" chemical and biological weapons quickly.

In his Feb. 5 presentation to the U.N. Security Council (search), Secretary of State Colin Powell said the Bush administration has estimated that Iraq has a stockpile of between 100 and 500 tons of chemical weapons agent — enough to fill 16,000 battlefield rockets.

Administration officials told Fox News that that assessment is still accurate and they pointed out that 100 tons of anthrax or some other agent could be hidden in one building alone.

"There are a lot of buildings, tunnels, and places to hide these weapons that we haven't even discovered yet," the officials said.

One senior official said Wednesday, "there are going to be a lot of people with egg on their face when we find this stuff … and we will."

The Iraq Survey Group (search) — a group of 1,300 weapons experts — is now on the ground in Iraq, following up on new leads coming from interrogations of regime Saddam Hussein's regime members, including that of Abid Mahmoud (search), Saddam's secretary and bodyguard, who officials say is "singing like a bird."

Now the second-in-command under Franks, Abizaid received a warm reception from the Armed Services Committee and is unlikely to face major obstacles to his confirmation by the full Senate.

Senators said his personal and professional background made him uniquely qualified for the high-profile position overseeing U.S. military operations from the Horn of Africa to Central Asia, including Iraq, Afghanistan and the Middle East.

Abizaid has experience from military operations in Kosovo, Bosnia and the 1991 Persian Gulf War. He is the grandson of Lebanese immigrants, fluent in Arabic, and holds a master's degree in Middle East studies from Harvard.

Abizaid said U.S. intelligence was extremely accurate in pinpointing Iraqi troop positions and in leading to the capture of 32 of the most-wanted Iraqis, but was "perplexingly incomplete" on weapons of mass destruction.

He said he remains confident that "at some point, it (the intelligence) will lead us to actual weapons of mass destruction."

Abizaid said U.S. forces had a lot of intelligence that it should expect weapons of mass destruction to be used against them as they neared Baghdad.

"I thought as we crossed what we termed the red line that we would overrun artillery units that had chemical warheads," he said. But no weapons were found.

Chairman John Warner, R-Va., suggested that the speed of the U.S offensive could have prevented Iraq from deploying the weapons, but Abizaid was doubtful.

"I believe that if we had interrupted the movement of chemical weapons from the depots to the guns, that we would have found them in the depots. But we've looked in the depots, and they're not there," he said.

Responding to a question about continuing violence against U.S. forces, Abizaid said: "We are certainly in for some difficult days ahead," but added that "it wouldn't be safe to say that the situation is going to continue to get worse."

He said it is "an open question" whether Saddam is alive, but that getting an answer is important.

"I believe that the Baathist Party's 30-year reign of terror will not come to an end easily until we can show them that not only can we get 32 of the 52 (most wanted), but we can get 52 of the 52," he said.

Fox News' Bret Baier and The Associated Press contributed to this report.