WASHINGTON - After years of delay caused by inadequate intelligence, the U.S. government decided just one day before the Sept. 11, 2001, terrorist attacks that it would try to overthrow the Taliban rulers of Afghanistan if a diplomatic push to expel Osama bin Laden from the country failed, the independent panel investigating the attacks reported Tuesday.

The plans were reported in May 2002 by MSNBC.com and NBC News, but the details and precise timing were revealed for the first time in the new report released Tuesday by the National Commission on Terrorist Attacks Upon the United States.

The report alleges that the Clinton and Bush administrations moved slowly against the al-Qaida terror network in the years before the attacks, partly because they lacked detailed intelligence that would have allowed a military strike and partly because they preferred to explore diplomatic alternatives. As a result, bin Laden and other al-Qaida leaders were able to elude capture repeatedly.

That conclusion was challenged in testimony by Secretary of State Colin Powell and Madeleine Albright, Powell's predecessor under former President Bill Clinton, both of whom said their respective administrations did everything possible to combat the shadowy al-Qaida.

Powell acknowledged, however, that top officials underestimated the danger to the United States itself. "Most of us still thought that the principal threat was outside the country," he said.

The testimony came as the commission began airing what appears certain to be a central issue in the presidential campaign, opening a two-day public hearing on the U.S. response to the growing al-Qaida threat before the deadly attacks on the World Trade Center and the Pentagon.

Bush told reporters Tuesday that he would have acted more quickly against al-Qaida if he had had information before Sept. 11 that a terrorist attack was imminent.

Three-phase plan to force bin Laden's expulsion

In the report, which was released at the outset of Tuesday's hearing, the commission said the plan that senior Bush officials agreed upon on Sept. 10, 2001, featured three phases aimed at forcing the Taliban to expel bin Laden:

The United States would initially use diplomacy to persuade the Taliban to expel bin Laden and, if that failed, conduct a covert program aimed at "encouraging anti-Taliban Afghans to attack al-Qaida bases."

If those steps failed, the senior Bush administration officials "agreed that the United States would seek to overthrow the Taliban regime through more direct action," the report said.

But before the plan could be submitted to the president, bin Laden's terrorists struck the World Trade Center and the Pentagon, killing nearly 3,000 people.

The commission faulted both the Bush and Clinton administrations for ignoring warning signs and failing to pursue significant military action that could have disrupted al-Qaida and its Taliban sponsors, who were becoming increasingly dangerous.

"This period [of diplomacy in the late 1990s] may have been the high-water mark for diplomatic pressure on the Taliban. The outside pressure continued. But the Taliban appeared to adjust and learn to live with it," the report found.

It found that the Clinton administration had indications of terrorist links between bin Laden and Khalid Sheikh Mohammed, the mastermind of the Sept. 11 attacks, as early as 1995 but that intelligence officials played down the evidence, which "was tightly compartmented in order to prevent leaks."

As a result, it said, years passed as the administration pursued diplomatic solutions. In 1995, for example, U.S. agents found Mohammed in Qatar, but he managed to escape while U.S. officials first sought a legal indictment, it said.  

William Cohen, Clinton's defense secretary, testified Tuesday that the Clinton administration recognized the dangers posed by al-Qaida and considered the United States to be "at war" against it. Three times after August 1998, U.S. officials considered using missile strikes to kill bin Laden, he said, but each time the intelligence was too sketchy to ensure success.

Albright echoed that assessment, saying Clinton was fully prepared to order military action to capture or kill bin Laden. "If we had had the predictive intelligence we needed, we would have done so," she said.

Warnings from Clarke cited

Bush inherited the problem when he became president in January 2001. But administration officials failed to act immediately on urgent warnings to take out al-Qaida targets by its counterterrorism adviser, Richard Clarke, the report said.

The hearing took on new urgency after a weekend bombshell by Clarke, a holdover from the Clinton administration, who charged that the Bush administration did not take the al-Qaida threat seriously before the Sept. 11 attacks and then focused on tying the strikes to Iraq.

In his testimony Tuesday, Powell issued an implicit rebuttal of Clarke, who was scheduled to testify Wednesday.

"President Bush and his entire national security team understood that terrorism had to be among our highest priorities, and it was," Powell said, but the Sept. 11 plot was too far advanced by the time Bush took office in January 2001.

"Those who were perpetrators of 9/11 ... already had their instructions. They had their plans in place," he said, adding that there was no indication that a military strike against al-Qaida's base of operations in Afghanistan would have caused the 19 hijackers to abort their plans.

Albright defends Clinton response

Albright, the first official to testify, defended the Clinton administration against accusations that it stalled, saying it "did everything ... we could think of" to eliminate the threat posed by al-Qaida.

Albright noted that Clinton authorized U.S. forces to kill bin Laden after the bombings of the U.S. embassies in Kenya and Tanzania in 1998 and ordered a retaliatory cruise missile attack on al-Qaida training bases in Afghanistan.

She said Clinton warned the Taliban that it would be held responsible for any further attacks against U.S. targets.

Albright urged commission members to ask Bush administration officials why they did not follow through on the threat after it was determined that the Oct. 12, 2000, attack on the guided missile destroyer USS Cole in Yemen was the work of al-Qaida.

"When there was proof that al-Qaida was connected [to the attack] ... why was there not a response?" she said.

Defense Secretary Donald Rumsfeld, testifying later, said military intervention would not have been a good idea. While it would have been a "bold stroke [that] sounded good," he said, the Bush administration had not yet put together a comprehensive policy for terrorism or any contingency plans.

Rumsfeld said he could not recall "any particular counterterrorism issue that engaged my attention" before Sept. 11, other than the possibility of using unmanned aircraft against bin Laden.

Cohen agreed, saying the public would not have supported launching a war before Sept. 11.

But a member of the commission, former Sen. Bob Kerrey, D-Neb., said that was no excuse.

"The fact that it's unpopular, that it's difficult, that our allies aren't with us, doesn't change the fact we have a serial killer on our hands," Kerrey said while questioning Cohen. "We had a round in our chamber, and we didn't use it."

Kerrey went on to denounce both administrations for letting al-Qaida and the Taliban off the hook.

"I keep hearing the excuse we didn't have actionable intelligence," he said. "Well, what the hell does that say to al-Qaida? Basically, they knew &emdash; beginning in 1993, it seems to me &emdash; that there was going to be limited, if any, use of military and that they were relatively free to do whatever they wanted."

Secret diplomacy

The preliminary report said that the U.S. government had determined that bin Laden was a key terrorist financier as early as 1995 but that efforts to expel him from Sudan stalled after Clinton officials concluded that he could not be brought to the United States without an indictment. A year later, bin Laden left Sudan and set up his base in Afghanistan without resistance.

The report said that in a previously undisclosed secret diplomatic mission, Saudi Arabia won a commitment from the Taliban to expel bin Laden in 1998. But a clash between the Taliban's leader, Mullah Mohammad Omar, and Saudi officials scuttled the arrangement, and the United States did not follow up.

Clinton designated CIA Director George Tenet as his representative to work with the Saudis, who agreed to make an "all-out secret effort," the panel said.

The Saudi intelligence chief, Prince Turki bin Faisal, using "a mixture of possible bribes and threats," received a commitment from Omar that bin Laden would be handed over. But Omar reneged on the agreement in September 1998 during a meeting with Turki and Pakistan's intelligence chief.

"When Turki angrily confronted him Omar lost his temper and denounced the Saudi government. The Saudis and Pakistanis walked out," the report said.

In conclusion, the report said "from the spring of 1997 to September 2001, the U.S. government tried to persuade the Taliban to expel bin Laden to a country where he could face justice," the report said. "The efforts employed inducements, warnings and sanctions. All these efforts failed."

The Bush administration then failed to "develop any diplomatic initiatives on al-Qaida with the Saudi government before the 9/11 attack," it said.

Commission staff described Saudi Arabia as "a problematic ally in combating Islamic extremism," noting its lax oversight of charitable donations that may have funded terrorists. Still, in spring 1998, the Saudi government successfully thwarted a bin Laden-backed effort to launch attacks on U.S. forces in that country, the report said.

Sensitive timing for hearings

The hearings come as Bush's re-election campaign is showcasing his role as a wartime president. And it follows explosive allegations in a book released Monday by Clarke, Bush's and Clinton's former counterterrorism coordinator.

Clarke said he warned Bush officials in a January 2001 memo, just as they were taking office, about the growing al-Qaida threat after the Cole attack but was put off by national security adviser Condoleezza Rice, who "gave me the impression she had never heard the term before."

Rice responded in a series of interviews Monday that she asked Clarke to come back with a more comprehensive strategy to eliminate al-Qaida, including military options rather than "pinprick strikes against training camps that had already been abandoned."

The commission's preliminary report released Tuesday offered some support for both accounts, saying Clarke pushed for immediate and secret military aid to the Taliban's foe, the Northern Alliance. But Rice and her deputy, Stephen Hadley, proposed a broader review of the al-Qaida response that would take more time, it said.

The 10-member commission invited Rice to testify, but she declined on the advice of the White House, which cited concerns over the constitutional separation of power involving its staff's appearing before a legislative body.

Rice did meet privately with commission members for four hours on Feb. 7 in what Ben-Veniste termed a "very useful interview," in which he found her "candid and forthcoming." Another panel member, former Rep. Tim Roemer, D-Ind., said the "tone and level of cooperation ... was productive." But Ben-Veniste and Roemer have both said they believe Rice should testify in public.

By MSNBC.com's Alex Johnson and Mike Brunker. NBC's Andrea Mitchell and Tracie Potts, The Associated Press and Reuters contributed to this report.