In a stunning setback for The Boeing Co., Northrop Grumman Corp. and a European aerospace company on Friday won a $30 billion to $40 billion contract to start replacing the aging fleet of Air Force aerial tankers.

The contract, announced by Air Force Secretary Michael Wynne, could be worth an estimated $100 billion as the Air Force replaces its fleet of roughly 530 mostly Eisenhower-era aerial tankers.

The EADS-Northrop Grumman tanker is based on the newer Airbus A330 airframe. The planes are built in Toulouse, France, with final assembly planned for a new plant in Mobile, Ala.

Boeing, which has built the Air Force tankers for the past half-century, had been heavily favored to win the competition.

The Air Force’s fleet of tankers will be replaced in three phases. The program will be the second largest Pentagon program ever, behind the $200 billion Joint Strike Fighter, said Loren Thompson, an analyst with the Lexington Institute, a military research center.

“I am extremely disappointed in the Air Force’s decision to choose Northrup Grumman/EADS over Boeing to make the critical new aerial-refueling tanker. From the beginning, the Air Force vowed to have an open competition process,” said Sen. Pat Roberts, R-Kan. “I look forward to seeing their justification for this unfortunate outcome. If this decision holds, it will be at the cost of American jobs and American dollars, if not our national security.”

Northrop Grumman teamed with the European Aeronautic Defense and Space Co., the parent company of Boeing’s fierce European rival, Airbus. EADS has been gunning to crack the U.S. defense market, and Northrop Grumman hadn’t produced a military plane since the B-2 Stealth bomber.

Both sides had engaged in heated public relations campaigns to promote their tankers.

EADS argued that the A330 was newer, larger and could carry more fuel, cargo and passengers. Boeing said the 767 was cheaper to operate, could fly into smaller airfields and would take up less ramp space.

The Air Force had agreed earlier to lease 100 767s for more than $23 billion. But the deal collapsed amid a 2003 procurement scandal that sent Boeing’s chief financial officer and a top Air Force acquisitions officer to prison. Boeing’s chief executive officer resigned. The investigation into the lease agreement was spearheaded by Arizona Sen. John McCain, who’s now the front-runner for the Republican presidential nomination.

Congress eventually will have to appropriate funding for the tanker program, and already there have been sharp words between Boeing and Airbus supporters over whether the plane should be built by a U.S. company or a foreign one.