OTTAWA — Canada will significantly weaken NATO's war against the Taliban when its troops leave Afghanistan in 2011, an influential American counter-insurgency expert has said.

Anthony Cordesman, who has advised NATO's current ground commander, U.S. Gen. Stanley McChrystal, said losing the experience and credibility of Canadian troops around the Kandahar region will undermine military efforts in a crucial battleground.

"It isn't simply a matter of troop levels," Cordesman said in an interview with The Canadian Press. "It's a matter of experience continuity; having shaped the security presence in one of the most critical provinces in the country."

"Would a Canadian departure seriously hurt NATO? The answer at least this point seems to be: Yes."

Cordesman said reluctant NATO countries need encouragement to "eliminate as many national caveats and restrictions on troops as possible" and that the U.S. government should dispatch additional troops to stem increasing violence in the war-torn country.

McChrystal sought out Cordesman's advice as part of a 60-day review of the military strategy NATO forces have adopted in Afghanistan. He is expected to appear before Congress in September.

While the U.S. has more than enough trained troops to replace Canada's 2,850, Cordesman said, diplomatic efforts towards Ottawa are intensifying because of the difficulty of replacing Canadian expertise.

"The experience Canada has gained and the effectiveness of its civil-military operations have been particularly critical," said Cordesman, an expert at the Center for Strategic and International Studies in Washington. He added that the NATO forces who replace Canadian soldiers in Kandahar "are not going to have the capabilities that Canada has developed over years of having been in the province."

"The fact is, just because you do not have the largest contingent in Afghanistan doesn't make the country's role unimportant."

Last week, NATO's new secretary-general pleaded with Canadian officials to agree to remain longer in the Central Asian country. Members of the Obama administration have also been hinting they would like Canadian troops to maintain their presence well in to the next decade.

But the Conservative government has shown few indications that it intends to extend the date for withdrawing Canadian combat troops beyond July 2011. Ottawa quickly replied to the secretary general's recent request by reaffirming the decision to pull out as scheduled.

On Tuesday, Defence Minister Peter MacKay said NATO's leadership can ask many other countries to contribute to the mission before additional participation is requested from Canada.

Michel Drapeau, an Ottawa lawyer and retired colonel, told CTV News Channel that Cordesman's comments will encourage defence lobbyists in Canada to step up pressure on Ottawa to extend its Afghan presence.

"This will only add fuel to the fire," he said. "The fact of the matter is, our troops have given an extraordinary commitment and sacrifices over the past. By the time we return it will be almost 10 years we will have been in Afghanistan."

"There's nothing in our constitution that says we have to be there forever," he said. Canadian troops "are tired, their families are exhausted, the equipment requires to be replaced."

"We have done our share."

With files from The Canadian Press