By Andrew Gray

WASHINGTON, Feb 25 (Reuters) - The United States will be able to ramp up supplies for thousands of extra troops being sent to Afghanistan even though convoys have come under attack in Pakistan, a top U.S. general said on Wednesday.

Air Force General Duncan McNabb, head of U.S. Transportation Command, said the attacks by militants in Pakistan had declined recently and the U.S. military had expanded its options for delivering supplies to Afghanistan.

But McNabb, whose headquarters is responsible for moving U.S. military supplies around the world, acknowledged that he worried about the security of the Pakistan routes.

"It's something that gives us great concern," he told a House (of Representatives) committee. "You don't want to make this a vulnerability," he added. "And I, quite frankly, do not think that it is. I think that we will get the stuff through."

Militants staged a string of attacks late last year on supplies trucked by commercial haulers through northwest Pakistan from the port of Karachi to U.S. and other foreign troops fighting a resurgent Taliban in landlocked Afghanistan.

Hundreds of trucks were destroyed in the attacks and several drivers were killed.

Earlier this month, suspected militants blew up a bridge in northwestern Pakistan's Khyber Pass, temporarily cutting the main supply route for Western forces in Afghanistan.

The U.S. military's logistical efforts were further complicated this month when Kyrgyzstan decided to shut down a U.S. air base in the central Asian country, a hub for moving troops and equipment into Afghanistan.

President Barack Obama, in his first major military decision, last week approved the deployment of 17,000 extra U.S. troops to Afghanistan.

MAJOR CHALLENGE

McNabb said getting supplies into Afghanistan through its rugged mountainous terrain was a major challenge, with essentially only five possible access points by land.

"You couldn't choose a harder place," he said.

McNabb said the U.S. military needed about 78 shipping containers to be trucked into Afghanistan daily to supply the 38,000 U.S. troops currently there and the routes through Pakistan could potentially handle three times that number.

Since the beginning of January, an average of 90 containers had been trucked in every day, McNabb said.

"What I do is make sure we're always beating 78," McNabb told the Seapower and Expeditionary Forces Subcommittee of the House Armed Services Committee.

The number of containers needed could rise by about 50 percent to sustain the larger U.S. force ordered in by Obama, he said.

The U.S. military sends food, water, fuel and construction supplies into Afghanistan by land but sensitive military equipment is transported by air, McNabb said.

About 75 percent of U.S. supplies for the Afghan war through or over Pakistan, the Pentagon says. But officials, alarmed by the attacks there, have sought in recent months to open up central Asian routes into northern Afghanistan.

Uzbekistan and Turkmenistan have agreed NATO non-military cargo for Afghanistan may pass through their territories, Russia's Interfax news agency reported on Wednesday. (Editing by David Storey)

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