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By Matt Spetalnick

KABUL, Dec 15 (Reuters) - President George W. Bush went into talks with Afghan President Hamid Karzai on Monday to assure him that the United States will stand by the war-torn country despite a transition of power at the White House.

Moving from one war zone to another, Bush flew secretly from Baghdad to Kabul, landing under cover of darkness for talks with Karzai and meetings with U.S. troops spearheading the fight against a resurgent Taliban.

"I want to be in Afghanistan to say thank you to President Karzai and let the people of Afghanistan know that the United States has stood with them and will stand with them," Bush told reporters before landing at Bagram Air Base, outside the capital.

On a farewell visit to Baghdad on Sunday, meant to mark greater security in Iraq after years of bloodshed, an Iraqi reporter called Bush a "dog" and threw his shoes at him.

After Air Force One touched down at Bagram air base outside Kabul under heavy security, Bush strode across the tarmac and into a giant tent where hundreds of troops greeted him with raucous cheers as he thanked them for their service.

"I am confident we will succeed in Afghanistan because our cause is just," he told them.

Bush reviewed a military honour guard with Karzai before they went into the heavily guarded presidential palace for talks.

Bush, who has already ordered a troop increase in Afghanistan, appeared to lend tacit support to President-elect Barack Obama's pledge to increase troop levels after he takes office on Jan. 20.

"I recognised that we needed more troops. President-elect Obama is going to make decisions on troops. And we've been calling on our NATO allies to put in more troops," Bush said.

Obama has promised to make Afghanistan a higher priority, saying the Bush administration has been too distracted by the unpopular Iraq war to pay Afghanistan the attention it deserves.

COOPERATE WITH PAKISTAN

Bush also said it was important for the United States to keep working with Pakistan to pressure militants along its border with Afghanistan. Osama bin Laden and his top lieutenants are believed to be hiding out in the remote, lawless region.

"If Pakistan is a place from which people feel comfortable attacking infrastructure, citizens, troops, it's going to make it difficult to succeed in Afghanistan," Bush said.

"The more we can get Pakistan and Afghanistan to cooperate, the easier it will be to enforce that part of the border regions," Bush added.

Bush was making his second trip to Afghanistan in the seven years since U.S.-led forces ended Taliban rule in response to the Sept. 11, 2001, attacks on the United States.

Around 65,000 international troops are in Afghanistan, including more than 30,000 from the United States, struggling to combat worsening insurgent violence that has sparked alarm in Washington and other Western capitals.

"No question that violence is up," Bush said. "But one reason why the violence is up is we're now putting troops in places where there hadn't been troops."

U.S. Army Gen. David McKiernan, commander of NATO forces and most U.S. troops in Afghanistan, has requested four more combat brigades and support units -- a total of more than 20,000 troops. One of those brigades is scheduled to deploy in January.

Washington's ability to send more forces to Afghanistan depends largely on being able to pull some of its nearly 150,000 troops out of Iraq, where security has improved sharply but commanders caution the situation remains fragile.

Resistance of some NATO partners to Washington's push for higher troop levels in Afghanistan has caused friction within the alliance.

"The mission is essential. We cannot achieve our objective of removing al Qaeda safe havens by kicking out Talibans and saying 'OK, now let's leave," Bush said.

Asked whether Karzai -- who is expected to stand for re-election next September -- was the right man to lead the fight, Bush said: "That will be determined by the Afghanistan people. That's the great thing about elections."

Asked whether Pakistan was doing its part in its border areas, Bush said Pakistani President Asif Ali Zardari was determined.

"He said so publicly and he said privately. He looked at me in the eye and said 'you don't need to talk to me about extremist violence. After all my wife got killed by extremists'."

Despite that, tensions between Washington and Islamabad have flared over U.S. drone strikes aimed at militants along Pakistan's border with Afghanistan.

Pakistan has complained that the strikes are a violation of its sovereignty, but Bush recently said he had made clear to Pakistan that the United States will do whatever is necessary to protect American soldiers and lives. (Reporting by Matt Spetalnick; Editing by Bill Tarrant and John Chalmers)

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