Terrorism was "an important issue but not an urgent issue" when President Bush took office in January 2001 up until the Sept. 11 terror attacks, former Bush and Clinton counterterrorism adviser Richard Clarke (search) testified Wednesday.

But "my impression was that fighting terrorism in general and fighting Al Qaeda, in particular, was an extraordinarily high priority in the Clinton administration. Certainly, there was no higher priority," said Clarke.

Later, Clarke also blasted the U.S.-led war in Iraq. "By invading Iraq, this president has greatly undermined the war on terrorism."

Clarke was the latest official from the current and previous White House administrations to testify before the National Commission on Terrorist Attacks Upon the United States, which is investigating fumbled military and diplomatic efforts surrounding the Sept. 11 attacks.

But of all those who went before the 10-person panel this week, Clarke has been the most controversial. After leaving the White House, where he had been publicly supportive of the Bush administration, Clarke wrote a new book leveling blunt criticism against Bush and his top aides.

"He needs to get his story straight," said Condoleezza Rice (search), Bush's national security adviser and Clarke's boss while he served in the administration.

Clarke began his testimony by addressing the families of Sept. 11 victims in the audience, saying, "Your government failed you."

"We tried hard but that doesn't matter because we failed and for that failure I would ask, once all the facts are out, for your understanding and for your forgiveness."

Officials Agree: Sept. 11 Likely Not Preventable

Officials from both the Bush and Clinton White Houses agreed that the deadly attacks were not preventable, even if Al Qaeda leader Usama bin Laden had been nabbed before Sept. 11.

"We were hit," said former President Clinton's national security adviser, Sandy Berger (search). "We must learn the right lessons so that it never happens again."

"Decapitating one person, even bin Laden in this context, I do not believe would have stopped this plot," said CIA Director George Tenet (search). "We certainly understand they [Sept. 11 hijackers] had the operational flexibility to decide what to do -- this plot was well on its way."

"Killing bin Laden would not have removed Al Qaeda's sanctuary in Afghanistan," Defense Secretary Donald Rumsfeld (search) testified Tuesday. "Moreover, the sleeper cells that flew the aircraft into the World Trade towers and the Pentagon were already in the United States months before the attack."

But that doesn't mean efforts weren't made, officials said, and people like Tenet said systems were put in place as early as 1996 to try to track bin Laden.

"Even if you're on the right track, you can still get run over if you're not going fast enough," Bush's deputy secretary of state, Richard Armitage, testified.

"Secretary Powell thought this [terrorism] was a real problem. But we don't have the luxury of ranking them [priorities] in order," Armitage added, saying there were many issues the Bush administration was trying to wrap its arms around when it came to the White House.

But "terrorism and counterterrorism were urgent," he said.

Clarke: Bush White House Frustrated Me

Clarke's book "Against All Enemies," which was released Monday, blasts the Bush administration's handling of Sept. 11 and Al Qaeda threats.

Even before Sept. 11, Clarke said he was "sufficiently frustrated" by Bush's approach to tackling terrorism, which he described as lacking in fervor. He said he talked terrorism more with Clinton's national security adviser than Bush's.

"My view was that this administration didn't listen to me -- either didn't believe me that there was an urgent problem or was unprepared to act as if there was an urgent problem," Clarke said.

Clarke was asked by panel members why, then, he defended Bush's terrorism policies.

"When you're on the staff of the president of the United States, you try to make his policies look as good as possible," Clarke said. "I was asked to highlight the positive aspects of what the administration had done and minimize the negative aspects of what the administration had done."

In August 2002, Clarke briefed a handful of reporters and described the handover of intelligence from the Clinton administration to the Bush administration and the latter's approach to Al Qaeda.

The White House allowed Fox News to name Clarke as the official giving the briefing. Foxnews.com provided a transcript of that briefing Wednesday.

The Bush team spent eight months formulating a plan to combat terrorism -- it was ready for the president's viewing on Sept. 4, 2001. That plan, Clarke said, could have and should have been instituted in February.

He also faulted U.S. intelligence agencies for not knowing more about the plot and said most officials thought an attack from Al Qaeda likely would take place abroad, either in Saudi Arabia or Israel.

"The fact that we didn't have intelligence that we could point to that said it could take place in the United States wasn't significant, in my view," Clarke said. "I didn't think the FBI would know whether or not there was anything going on in the United States by Al Qaeda."

Several panelists said they were taken aback by the brouhaha surrounding Clarke's book and his allegations, since his closed-door sessions with the commission panel were completely different in tone.

"What I don't understand is if you had these deep feelings and deep concerns … in the Bush administration that you didn't advise the [Sept. 11] joint inquiry," said former White House counsel Fred Fielding.

"You've got a real credibility problem," John Lehman, former Navy secretary under President Reagan, told Clarke, calling the witness "an active partisan selling a book."

We Must Be 'Relentless' Against the Threat

Tenet vowed that "nothing I have worked on is more important or more personal" than determining how Sept. 11 could have happened and said, "the war ahead is going to be complicated and long." Sept. 11, 2001, marked just the "beginning of the age of catastrophic terrorism," Berger said.

"While we were on the offensive prior to 9/11 … the country, with all of its capabilities, is now much more orchestrated into an offensive mix that is relentless," added Deputy Central Intelligence Director John McLaughlin (search). "One thing the American people need to understand is we are still at war, every single day … we are acting on intelligence to take down terrorists all across the world."

During the Clinton years, 67 Americans lost their lives in terrorist-related incidents; 35 of those died at the hands of Al Qaeda, Clarke noted, but still, people asked him, "why are you obsessed with this organization?"

"That's the kind of mindset that made it difficult for us," he testified.

One criticism of the Clinton White House was that its idea of military action was "pounding sand," or just sending cruise missile or bombs from afar to target not much more than dirt. That strategy is often contrasted with "boots on the ground," where more troops are physically sent in to take out the targets.

But "there should be no question as to what Clinton's intent was when he fired 60 Tomahawk missiles at bin Laden" in 1998, Berger said. "I can assure you, they weren't serving an arrest warrant."

Officials from both the administrations said they were ready to take appropriate military action and all agreed that without Sept. 11, there wouldn't have been enough public or congressional support for invading Afghanistan.

The commission released one report Wednesday that said CIA efforts to stop bin Laden before Sept. 11 were hindered by confusion over whether intelligence officers were allowed to kill the Al Qaeda leader.

Another panel report said U.S. officials' pursuance of diplomacy over military action allowed bin Laden and other Al Qaeda leaders to elude capture.