President Bush and Secretary of State Condoleezza Rice expressed concern Thursday that the commitment of NATO allies in Afghanistan may be flagging and warned against allowing the country to again become a cauldron for extremism.

In separate news conferences, Bush and Rice made clear that the United States cannot accept Afghanistan as a failed state where al-Qaida is able to regroup and possibly use as a stage to launch future terrorist strikes like the Sept. 11, 2001, attacks.

"My biggest concern is that people say, 'Well, we're kind of tired of Afghanistan and, therefore, we think we're going to leave'," Bush said at the White House. "That would be my biggest concern."

Later, Rice made the same point at a joint news conference at the State Department with Canadian Foreign Minister Maxime Bernier. The Canadian government and parliament will begin debate early next year on whether to extend Canada's military operations in Afghanistan beyond its current mandate that ends in February 2009.

"Afghanistan as a failed state was, of course, very much the near-term cause for the emergence of a trained and capable al-Qaida," Rice said. "It is an absolutely essential mission to stabilize Afghanistan. We learned the hard way what happens when we allow a failed state to emerge in Afghanistan."

"It was the United States that was attacked on September 11 but, of course, it could have been any of us, and it has been others, as well," she said. "We just have to remember that in the war on terror, what we're trying to do is to help states like Afghanistan become self-sustaining states that are not going to be safe havens for terrorists."

The Bush administration has launched a wide-ranging review of its policy in Afghanistan to ensure that gains made since the radical Islamist Taliban regime was ousted in 2001 are not lost and to bolster Afghan President Hamid Karzai's nascent government. Bush is holding regular secure videoconferences with Karzai to discuss the situation.

Bush and Rice lavished praise on Canada, other NATO allies and non-alliance members that have troops in Afghanistan.

"I would like to praise the Brits, the Canadians, the Dutch, the Danes and other countries for their contributions -- the Aussies for their contribution of shooters, fighters, people that are willing to be on the front line of this battle," Bush said. "These are brave souls."

Australia is not a NATO member but in her comments Rice stressed the need of "the entire alliance to share in the responsibilities of this most important mission that NATO has taken on ... we are working with all of the allies to make sure that the responsibilities are spread more evenly."

Speaking specifically about Canada, which has 1,700 troops in and around the southern Afghan city of Kandahar where insurgent activity is high, Rice called Ottawa's contribution "invaluable and effective." "Canada is sharing in that responsibility. Canada is pulling its weight."

Because of their deployment in Kandahar, Canadian troops are taking high numbers of casualties, with 73 combat deaths, and there is growing public unease in Canada about the mission. A panel appointed by Prime Minister Stephen Harper is due to present a report on Canada's role in late January after which parliament will consider how the country should proceed.

Bernier said he hoped "that will be a vote to have a strong commitment for the international community."

"Yes, we suffer a lot of casualties," he said. "But that being said, we still have to be sure that this part of the country will be secure. You cannot have economic development without security. You cannot have prosperity without security. It's a dangerous mission, but it's a mission that we're proud of."

In addition to fears that Canada night waver in its commitment, the Bush administration is concerned that other members of NATO are not stepping up to do their fair military share in Afghanistan.

Defense Secretary Robert Gates has been pressing for months -- without success so far -- to get 16 more helicopters into southern Afghanistan to relieve a U.S. helicopter unit that will be leaving soon. He is also looking to fill other needs, including 3,500 NATO trainers for the Afghan police as well as a minimum of three battalions of ground troops.

But last week in Scotland, at a NATO conference on Afghanistan, Gates said the administration had decided to tone down its appeals to NATO allies for more troops and other aid.

After two days of talks in Edinburgh with his counterparts from Britain, Canada and five other NATO countries whose troops are doing the bulk of the fighting in Afghanistan's violent south, Gates said he would continue making the case for greater allied military assistance.

However, he said he would be doing it differently, keeping in mind the "political realities" faced by some European governments whose people may see less reason to intervene in Afghanistan.

The United States has the largest foreign troop contingent in Afghanistan now with about 26,000. while Britain is the second-leading contributor with some 7,800. Gates has said there are no short- term plans to fill gaps left by NATO allies with more U.S. soldiers.