WASHINGTON – Under sharp questioning, national security adviser Condoleezza Rice insisted Thursday that President Bush fully understood the threat of terrorism before Sept. 11, 2001, but no intelligence foretold the deadliest attack ever on American soil.

Disputing criticism that Bush was negligent, Rice told a national commission “there was no silver bullet that could have prevented” the attacks that killed more than 3,000 people in New York, Pennsylvania and Washington, D.C.

Broadcast live around the world, the hearing turned contentious as Democratic members questioned why alarms didn’t ring when Bush was presented with an Aug. 6 classified memo titled “Bin Laden determined to attack inside United States.”

Former Sen. Bob Kerrey, a Democratic member of the commission, described the memo as saying that “the FBI indicates patterns of suspicious activity in the United States consistent with preparations for hijacking.”

Rice dismissed the document as “historical information based on old reporting” and said it did not warn of attacks inside the United States.

Commission members unanimously asked the White House to declassify the memo, whose title had not been revealed previously. Sean McCormack, a National Security Council spokesman, later said, “We have every intention to declassify it at this time.”

Relatives of victims killed on Sept. 11 sat in the audience behind Rice, scribbling notes and shaking their heads at times as she rebutted accusations by former counterterrorism aide Richard Clarke that Bush had fumbled opportunities to eliminate al-Qaida.

Unlike Clarke, Rice offered no apology for the government’s failure to prevent the attacks.

“Accountability, ma’am, accountability,” called out Carie Lemack, whose mother died on the first hijacked plane to hit the World Trade Center. After three hours in the witness chair, Rice shook hands with a few family members and then reached out to embrace a few more.

With much at stake for the president, Rice appeared composed and unruffled even as members challenged her responses and accused her of filibustering with long answers. Rice carried the responsibility of defending Bush’s credibility on the issue he has made the cornerstone of his re-election campaign.

After hearing from Rice, the commission met with former President Bill Clinton for more than three hours and said he was “forthcoming and responsive to questions.” Bush and Vice President Dick Cheney are to be questioned soon, also in private.

Rice, recalling a rash of vague warnings over the summer, said, “One of the problems here was there really was nothing that looked like it was going to happen inside the United States.” She said the threats pointed overseas to possible targets in the Persian Gulf, Israel or perhaps the summit in Genoa, Italy, of leaders of industrialized nations.

Bush and his wife, Laura, watched the testimony on television from their vacation home in Texas.

Rice was pressed on whether she had talked with the president about the existence of al-Qaida cells in the United States after being alerted by Clarke. She said she couldn’t recall.

Rice also was challenged on why Bush’s national security team met 100 times before it took up the subject of terrorism and whether she bore responsibility for the failure of FBI offices nationwide to be alerted about increased threats before Sept. 11.

After swearing to testify truthfully, Rice sat alone at the witness table, her hands laced in front of her on a red tablecloth as she read a prepared statement.

Rice said the United States, as far back as the Reagan administration more than 20 years ago, mounted an insufficient response to the gathering threat of terrorism. “The terrorists were at war with us but we were not yet at war with them,” Rice said.

Historically, democratic societies have been slow to respond to threats, she said, citing provocations before World Wars I and II.

“Tragically, for all the language of war spoken before Sept. 11, this country simply was not on a war footing,” Rice said.

Even so, Rice said, Bush “understood [the] threat and he understood its importance.” She said Bush came into office determined to develop a “more robust” policy to combat al-Qaida and told his national security adviser he was “tired of swatting at flies.”

Picking up on her testimony, Kerrey noted that Bush failed to order a military strike in response to a 2000 attack on the destroyer USS Cole that killed 17 U.S. sailors three months before Bush took office.

“Dr. Rice, we only swatted a fly once. … How the hell could he [Bush] be tired?” Kerrey asked. That was a reference to a 1998 missile strike Clinton ordered against suspected terror training camps.

Former Gov. Jim Thompson, a Republican commission member from Illinois, also expressed unhappiness about Bush’s failure to respond to the Cole. “Blowing up our destroyers is an act of war against us, is it not?” he asked.

Rice said the administration decided not to respond “tit for tat” with an inadequate response that would simply embolden terrorists.

Rice’s testimony, under oath and on live national television, came after weeks of White House resistance. Bush yielded after repeated public requests from members of the commission – as well as quiet prodding by Republicans in Congress – that an on-the-record rebuttal was needed in response to Clarke’s explosive charges.

Clarke told the commission last month that the Bush administration gave a lower priority to fighting terrorism than had Clinton and that the decision to invade Iraq undermined the war on terror.

Clarke, interviewed on ABC, complimented Rice for a “very good job” in her testimony and challenged her on only one factual point. He said he had asked “several times” before the Sept. 11 attacks to brief Bush on terrorism, while Rice said he had not.

The hearing turned testy when Democratic commission member Richard Ben-Veniste asked Rice if she had passed along information to Bush from Clarke about al-Qaida cells in the United States.

Rice said she wanted to address other issues first, and she and Ben-Veniste took turns cutting each other off in mid-sentence. She eventually said she did not recall if she had told Bush.

They also clashed on the Aug. 6 memo.

“I would like to finish my point here,” Rice said.

“I didn’t know there was a point,” Ben-Veniste snapped.

Under questioning, Rice acknowledged that she had spoken too broadly once when she said that no one had ever envisioned terrorists using planes and crashing them into buildings. She said that aides came to her within days and said there had been reports or memos about that possibility, but that she hadn’t seen them.

Pointing a finger of blame, she said that senior officials “have to depend on intelligence agencies to tell you what is relevant.”

“In hindsight,” Rice said, “if anything might have helped stop 9-11, it would have been better information about threats inside the United States, something made difficult by structural and legal impediments that prevented the collection and sharing of information by our law enforcement and intelligence agencies.”

Asked to rebut Clarke’s claim that Bush pressed him to find an Iraq connection to the suicide hijackings, Rice said she did not recall such a discussion, but that “I’m quite certain the president never pushed anybody to twist the facts.”

Rice insisted that the administration did all it could to prevent Sept. 11. “I’ve asked myself a thousand times what more we could have done,” she said.