WASHINGTON  The Air Force, in a stunning upset against the Boeing Company, awarded a $40 billion contract for aerial refueling tankers on Friday to a partnership between Northrop Grumman and the European parent of Airbus, putting a critical military contract partly into the hands of a foreign company.

The contract, one of the largest at the Pentagon, is initially valued at $40 billion but has the potential to grow to $100 billion. It is also a sign of the growing influence of foreign suppliers within the Pentagon and breaks a relationship that has lasted decades with Boeing, which had built the bulk of the existing tanker fleet and had fought hard to land the new contract.

Under the contract, Northrop and the European Aeronautic Defense and Space Company would build a fleet of 179 planes, based on the existing Airbus 330, to provide in-air refueling to military aircraft, from fighter jets to cargo planes. It gives a huge lift to Airbus, whose commercial aviation program has suffered a number of setbacks in recent years. While final assembly of the craft would take place at an Airbus plant in Mobile, Ala., parts would come from suppliers across the globe.

At a news conference, Air Force officials said that the creation of domestic jobs was not a factor in the decision. In response to questions about possible negative reaction to the deal in Congress, Gen. Arthur J. Lichte, head of the Air Force’s Air Mobility Command, said, “This will be an American tanker, flown by American airmen with an American flag on its tail and, every day, it will be saving American lives.”