With more than 500 international troop deaths in 2009, the war is becoming more deadly for foreign and Afghan troops alike as it drags into its ninth year since the Islamist regime was toppled in 2001.
Diplomats in Kabul say without the Western military presence, Karzai's government would soon collapse as the Taliban spreads its footprint across the country and setting up shadow administrative and judicial systems.
While being propped up by Western forces, set to rise this year to 150,000, and billions of dollars in annual aid, Karzai told Al-Jazeera Television his job is "to win the hearts and minds of the Afghan people".
"I have to win the hearts and minds of the Afghan people, I have to be legitimate and have the trust of the Afghan people if I am to be a good president," Karzai said.
"With the international community, I don't have to have their favour. They are here for a purpose, which is the fight on terror, and we are working with them for a purpose, which is the stability and safety of Afghanistan, so we have a common purpose."
Karzai began a second five-year term in November after being declared winner of an August president poll that descended into a ballot-stuffing farce, with investigators finding about a million votes for Karzai were fake.
In the interview, he said Afghanistan is "a good model" of democracy and has "done well" in education and economy -- despite the fact that millions of children do not go to school, extremists' intimidation limits girls' education and the economy is based principally on the illegal poppy trade.
But, he said, "in terms of security we have failed".
As the US and NATO prepare to send in almost 40,000 more troops and adjust the war strategy from a concentration on the battlefield to development and reconstruction, Karzai said they must also help build Afghan security forces.
"If these forces are coming only to chase the Taliban at the cost of Afghan civilians, of course that's not going to produce any good consequences for us," he said.
"We are also seeking that they must provide better training and equipment to Afghan forces and police so that we can soon start to take responsibility for the security of our country."
A distinction must be drawn, he said, between what he called "mainstream Taliban" -- unemployed youths who fight for cash -- and "terrorists".
"We don't want to undermine the Taliban, we want them to come and live a peaceful life in their own country. We want to undermine the terrorists."
US President Barack Obama has said he wants to begin withdrawal of troops in mid-2011, conditional on the ability of the Afghans to do the job themselves.
As billions of dollars are poured into training Afghan security forces, with the aim of boosting the army to 400,000, Obama's announcement is "an incentive", Karzai said.
"Afghanistan must very soon begin to provide for its own security... so we should speed up efforts to have our own forces, security and means to defend our country. I hope our international partners will support us to that end."
He said a recent militant attack on a US base near the Pakistan border -- which killed eight people, including seven CIA agents -- was "condemnable" but used the interview to criticise foreign troops for civilian casualties.
It is a touchstone issue for Karzai, who in recent weeks has used it to bolster his own popularity with a populace weary of war and quick to blame Western forces, though most civilian deaths are caused by the Taliban.
"I want the NATO countries to understand that the war on terror is not in the Afghan villages, it's not in the pursuit of every man that's wearing a turban and has a beard and is wearing the national dress of Afghanistan.
"These are the citizens of this country and they must be respected -- and then we will have peace and success," he said.
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