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Obama administration officials are showing growing frustration at Pakistan’s refusal to reopen ground routes used to move fuel and other war supplies into Afghanistan, a six-month standoff that the White House had hoped to resolve before the NATO summit that starts here today.

Secretary of State Hillary Rodham Clinton is scheduled to meet with Pakistani President Asif Ali Zardari on the sidelines of the summit, which will chiefly focus on winding down the war in Afghanistan. But White House officials ruled out a meeting between Zardari and President Obama, in an apparent sign of their displeasure at what they view as Pakistan’s intransigence.

NATO Secretary General Anders Fogh Rasmussen cancelled a meeting with Zardari, citing the Pakistani leader’s late arrival in Chicago. And Pentagon officials said Defense SecretaryLeon E. Panetta would meet officials from five countries in Central Asia that have provided an alternative, but considerably more expensive, northern land route for NATO supplies since Pakistan closed its roads last fall.

After weeks of closed-door negotiations, U.S. officials did not deny that they are seeking to send the Pakistanis a public message.

“If they’re feeling a little bit of pressure this weekend, they should,” said a U.S. official, who spoke on condition of anonymity because of diplomatic sensitivities. “The U.S. and NATO are ready to move beyond this issue.”

Pakistan closed its roads to trucks that supply NATO forces in Afghanistan after a mistaken U.S. air attack on Pakistani border posts killed two dozen Pakistani troops last November. The incident capped months of crises between Washington and Islamabad that added intense pressures to the two nation’s long-fraught relationship.

Pakistan officials recently demanded that the United States and NATO pay more than $5,000 for each truck entering its territory, a substantial increase over the previous $200 charge. In an interview last week, Panetta all but ruled out paying that much although U.S. officials are willing to pay a higher rate than before to reopen roads from the port of Karachi to the Afghan border.

Pakistani officials also have demanded a formal U.S. apology for the border attack. The White House has expressed regret for the incident, but has refused to apologize, arguing that both sides were at fault.

If Pakistan doesn’t reopen the routes, NATO will face additional difficulties and expenses as it seeks to withdraw combat forces and military equipment over the next 2 1/2 years.

Panetta’s meeting with officials from Kazakhstan, Uzbekistan, Turkmenistan, Kyrgyzstan, and Tajikistan is “to thank them for the northern routes,” the U.S. official said, adding “it’s not really directed at the Pakistanis.”

Russia also permits shipments across its territory but did not send senior officials to Chicago.

U.S. officials have reported recent progress in the effort to reopen the supply lines, clearing the way for Zardari to accept a late invitation to the NATO summit.

Briefing reporters on Air Force One as the president flew to Chicago Saturday night, Ben Rhodes, the deputy national security advisor, said the White House is confident a deal will be reached. But he made clear U.S. officials don’t expect an imminent break-through.

“We’re not anticipating necessarily closing out those negotiations this weekend,” Rhodes said. He added, “A lot of it is happening, frankly, at the working level between our governments.”