Northrop Grumman Corp. and its European partner EADS Co. said Thursday they will stay in the running for a massive Air Force contract to build a new line of refueling tankers — work the companies would base in Mobile, Ala.

The companies in recent weeks had threatened to bow out of the bidding, arguing that the specifications the Air Force established favor a plane made by Boeing Co., the only other company competing for the job. After reviewing contract specifications over the past week, they decided to continue chasing the contract.

“They have determined that they are going to compete for the tanker and do everything in their power to hopefully come back with a win,” said Rep. Jo Bonner, a Republican who represents the Mobile district where the companies have said they would build the plane if they win the contract. “They believe they can compete in this environment.”

“You’re looking at something that’s going to be going on probably for several decades, so it’s a tremendous opportunity,” he said.

The initial contract for 179 planes is worth an estimated $40 billion, the Air Force says. The winning bidder could have a leg up on more than $100 billion in work as the Air Force gradually replaces a 530-plane fleet.

Boeing would build the planes — based on its familiar 767 — in Washington state. The Northrop/EADS team would offer a modified version of the Airbus A330 plane, to be built in Mobile’s Brookley Field Industrial Complex.

The job could bring more than 1,000 jobs to the area.

Local and state officials last year rolled out a $110 million package of incentives to help lure the project.