The Air Force is trying to decide whether to approve a contractor's $520 million offer to improve the B-1 bomber or whether to try another solution to the troubled plane's electronic problems.

"We just got the (Eaton Corp.) proposal in the last month. We're looking at it and we're looking at other alternatives," said Air Force Maj. Gen. Michael D. Hall."We're going to put together a plan by the end of the year, but at this point, we're not sure which option we will pick," Hall said Tuesday.

Hall commented shortly after Charles Barron, a representative of Eaton, said it would cost $520 million for Eaton to improve the electronic defensive systems aboard the 100 B-1s purchased by the Air Force.

That $520 million would be atop the $3.5 billion Eaton contract already spent by the Air Force for the sophisticated computer systems that form the brains of the swing-wing plane's defenses.

The comments were made at a Boston University seminar on the B-1, which has been the subject of criticism ever since it was resurrected by President Reagan seven years ago.

President Carter terminated the plane 11 years ago, but Reagan reversed that decision, saying the B-1 was needed as a replacement for the aging B-52s that are the heart of the U.S. nuclear bomber force. Reagan also decided at the same time to go ahead with the radar-evading "stealth" bomber, which is known as the B-2.

In 1981, Reagan told Congress that the 100 B-1s could be purchased for $20.5 billion, a figure that has grown to $28 billion through inflation.

All 100 of the planes, model B-1Bs, have been delivered to the Air Force, but the service has discovered that their electronic "counter-measures" systems need to be improved or the planes won't make it through Soviet defenses and return should they be used during a nuclear war.

The costs to improve the B-1 would be in addition to the $28 billion already spent on the planes and some critics, such as Rep. Les Aspin, D-Wis., chairman of the House Armed Services Committee, have suggested that Congress should decide whether to go ahead with the improvements or spend the money for other weapons.

Rep. Dave McCurdy, D-Okla., a member of the House Armed Services Committee, told the seminar, "the problems with the B-1B are real and have to be fixed."