And as Emirates, the largest of the Gulf airlines, expands its flights to the United States, some aviation analysts say Delta's arguments are gaining traction. "This is a legitimate complaint," said Richard L. Aboulafia, an aviation consultant at the Teal Group in Fairfax, Va.

Mr. Aboulafia, the aviation analyst, said that Emirates and Etihad Airways, both based in the United Arab Emirates, had already expanded more significantly into Europe, causing problems for European airlines on routes to Asia. "I think that, in the minds of Delta executives, they've seen the future, and it looks like Europe," he said.

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Given the various costs in running an airline, he said, it can be hard to quantify that "a slightly lower capital cost on a plane played a key role in driving you out of a market." But, he said, European authorities had "added insult to injury" by focusing more on providing credit guarantees to help Airbus sell its largest plane, the A380, to the Middle Eastern carriers than on protecting their own airlines

The talks give Dubai-based Emirates leverage as it pushes Airbus Group to upgrade its A380 with fuel-efficient engines, said Richard Aboulafia, an aerospace analyst at Teal Group. Boeing would gain momentum for a storied jet with few sales prospects aside from replacing the Air Force One fleet, he said. “It would keep the -8I going through the decade and deliver an unpleasant blow to the A380 that’s long overdue,” Aboulafia said of a potential Emirates order.