The U.S. Air Force has boosted the potential value of Northrop Grumman Corp's contract to support the radar-evading B-2 bombers by more than 50 percent to $9.5 billion.

It raised the ceiling on the contract which was originally set at $6.1 billion by $3.4 billion, the Defense Department said on Wednesday.

At the same time, Los Angeles-based Northrop said it had received a U.S. Navy contract valued at roughly $2.4 billion for the refueling and overhaul of the Theodore Rossevelt, a nuclear-powered aircraft carrier.

The Pentagon, in its daily contract digest on Wednesday, did not specify the previous ceiling value of Northrop's bomber contract. The United States deploys 20 B-2s.

Work on the aircraft carrier is scheduled to last more than three years and will be the ship's one and only refueling and complex overhaul in a 50-year life span, Northrop said.

The Roosevelt is the fourth ship of the Nimitz class to undergo this major milestone.

More than 3,800 Northrop Grumman Shipbuilding employees would be working aboard the carrier during peak periods of the project, the company said.

Northrop shares closed down 46 cents to end the day's trade on the New York Stock Exchange at $48.90.

(Reporting by Jim Wolf. Editing by Robert MacMillan, Leslie Gevirtz)