CHICAGO; The Obama administration may be not be able to strike a long-awaited agreement with Pakistan to help supply Western soldiers in Afghanistan as hoped in time for a major NATO summit in Chicago this weekend, a U.S. official said. “There’s a distinct possibility that we may not see an agreement before the end of this weekend,” the U.S. official said on condition of anonymity. “But talks are progressing and we do expect to reach a deal in the near future.” Earlier this week, as Pakistani President Asif Ali Zardari accepted a last-minute NATO invitation to the May 20-21 summit, many U.S. officials were optimistic they could finally make a deal to reopen key NATO ground routes into Afghanistan. Pakistan shut the routes in protest when U.S. aircraft killed 24 Pakistani soldiers along the Afghan border in November. Zardari’s appearance at the summit was seen as a potential breakthrough after the border deaths plunged perennially poor U.S.-Pakistan ties into a deep freeze for months. Now, as the two countries continue to disagree about details of a possible deal, that optimism appears to have faded. NATO nations, grappling with severe fiscal pressure at home, are anxious to reach an agreement under which Pakistan would allow NATO trucks to once again travel on Pakistani roads, in part because shipping supplies into land-locked Afghanistan from the north is much more expensive. Being able to transit across Pakistan becomes even more important as U.S. commanders prepare for the monumental logistical task of withdrawing most of the 128,000 NATO soldiers in Afghanistan – and the equipment they have accumulated since 2001 – by the end of 2014. Negotiations between U.S. and Pakistani officials in Islamabad have dragged on. From the beginning, Zardari’s government has demanded a high-level apology for the border deaths, which NATO said were accidental but which enraged Pakistanis. The Obama administration, loathe exposing itself to further Republican criticism, has refused to apologize. The U.S. official said a “wide gulf” remained on the amount NATO nations would be charged for transporting equipment into Afghanistan, the central stumbling block in those talks. Pakistan says its roads require millions of dollars in repairs after years of NATO truck going back and forth. The amount that Pakistani officials believe should be charged is far higher than what U.S. officials have offered. “The fees proposed by the Pakistanis are unacceptable, not just to the United States but to our NATO allies,” the official said. Lack of an agreement could add strains to interactions between President Barack Obama and other senior U.S. officials and Pakistani leaders during the summit. U.S. officials have long complained that Pakistan has failed to act sufficiently against militants fighting U.S. troops in Afghanistan. The White House said on Thursday that Obama had no plans for a one-on-one meeting with Zardari. Still, Zardari’s government supports reopening the supply routes once a deal can be reached that satisfies both sides. For that reason the Obama administration expects to ultimately find an arrangement on the supply routes and on the precise amount of U.S. military assistance Washington owes Pakistan.