WASHINGTON, March 27 (Reuters) - The United States has escalated air strikes against al-Qaeda fighters operating in Pakistan's tribal areas fearing that support from Islamabad may slip away, The Washington Post reported on Thursday.

U.S. officials, who were not identified, said Washington wants to inflict as much damage as it can to al Qaeda's network now because Pakistani President Pervez Musharraf may not be able to offer much help in the months ahead.

Musharraf, a vital U.S. ally in the campaign against terrorism who has generally supported such strikes, has seen his power wane dramatically over the past year.

Over the past two months, U.S.-controlled Predator aircraft have struck at least three sites used by al-Qaeda operatives, the Post reported.

About 45 Arab, Afghan and other foreign fighters have been killed in the attacks, all near the Afghan border, U.S. and Pakistani officials were cited as saying.

Neither U.S. nor Pakistani authorities officially confirm U.S. missile attacks on Pakistani territory, which would be an infringement of Pakistani sovereignty.

Many al Qaeda members, including Uzbeks and Arabs, and Taliban militants took refuge in North and South Waziristan, as well as in other areas on the Pakistani side of the border after U.S.-led forces ousted the Taliban in Afghanistan in 2001.

According to the Post, the goal was partly to try to get information on senior al-Qaeda leaders, including Osama bin Laden, by forcing them to move in ways that U.S. intelligence analysts can detect.

Citing an administration official, the report said the campaign was not specifically designed to capture bin Laden before U.S. President George W. Bush leaves office in January.

"It's not a blitz to close this chapter," a senior official who spoke on the condition of anonymity told the newspaper. "If we find the leadership, then we'll go after it. But nothing can be done to put al-Qaeda away in the next nine or 10 months. In the long haul, it's an issue that extends beyond this administration."

(Writing by JoAnne Allen; Editing by Eric Beech)

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