The Air Force has a number of options if it wants to improve the B-1 bomber, and some of the plans could cost up to $3.4 billion, according to a report by the non-partisan Congressional Budget Office.

The CBO report released Monday was the newest entry in the long debate over the plane, which is defended by the Air Force and attacked by critics who say it can't do the job for which it was designed.A chief critic is Rep. Les Aspin, D-Wis., chairman of the House Armed Services Committee, who said the study would be "a primer for the debate to come on the expensive airplane's future."

"We have to decide first if it's worth it to fix the B-1B's problems, and then we have to decide what, if anything, to do about the expected Air Force requests for enhancements," Aspin said in a statement.

Two weeks ago, Aspin said it might be necessary to halt spending on the bomber rather than pay for expensive repairs.

But the Air Force saw the report in a different light.

Capt. Jay DeFrank, a spokesman for the service, said, "The CBO addresses a shopping list of possible enhancements, the vast majority of which were not requested by the Air Force. We constantly evaluate all systems, including the B-1B, for their ability to meet evolving threats and request enhancements as necessary."

The B-1's chief problems concern electronic countermeasures, the highly sophisticated system used to defend the plane against attack.

Aspin and other critics say there are questions about whether the B-1 could perform adequately its mission of flying into the Soviet Union and delivering a load of nuclear bombs. But the Air Force says the B-1 will be a success.

The CBO said "a sophisticated weapons system like the B-1B bomber is never really complete. Even as the Air Force seeks to correct problems in the original B-1B design, the service is considering enhancements to improve the bomber's capability."

The CBO study spelled out four possibilities. One would improve B-1 navigation and communications and redesign other electronic systems and would cost between $1.2 billion and $1.7 billion.