Lockheed Martin Corp. and The Boeing Co., the top two U.S. military contractors, are competing for an Air Force program valued at $1.5 billion to replace cracking wings on aging A-10 anti-tank aircraft.

The contract, which calls for new wing sets on about 200 planes, would be awarded over 10 years. The Air Force plans to select a winner around March, Boeing spokeswoman Madonna Walsh said. Boeing and Lockheed submitted their bids Jan. 17, Walsh and Lockheed spokesman Greg Caires both said Monday.

Both companies are looking to upgrades and modernization of aging military aircraft to keep military revenue growing as the Pentagon tightens spending on new, more expensive airplanes. The A-10, known as the Warthog, is a low-flying, ground-attack aircraft capable of maneuvering at slow speeds. It has been used in Iraq to support troops and attack armored vehicles.

Lockheed, based in Bethesda, Md., already has a contract valued at more than $2 billion that it won in 1997 to upgrade A-10 aircraft and install new cockpit electronics, Caires said. Lockheed is bidding for the wing work with Los Angeles-based Northrop Grumman Corp.

Boeing, based in Chicago, plans to do the A-10 work at facilities in Georgia, Missouri and Utah if it wins the contract. The plane, originally made by Fairchild Republic, was first delivered in 1976. The Air Force received the last A-10 in 1984.

Spirit Aerosystems Holdings Inc. also may bid on the work, Boeing's Walsh said. A Spirit Aerospace spokeswoman declined to comment on whether the company is bidding on the contract.