The majority of the Air Force's B1-B bomber fleet is being temporarily grounded on a daily basis because of a continuing shortage of parts, a General Accounting Office report released Saturday said.

The shortage has resulted in a cannibalization of parts, limited air crew training, and a reduction in the bombers' readiness to carry out its missions, the report said. The Air Force responded that it is "making progress in ensuring adequate parts are available" and that the bomber is performing its missions.The GAO report to the House Armed Services Committee was a follow-up to a June 1987 report that said spare parts shortages were causing temporary groundings of B-1B aircraft.

At a cost of $27 billion, the Air Force acquired 100 of the sleek, low-flying bombers designed to penetrate Soviet air defenses in wartime.

In its latest review, the GAO found that the Air Force "has initiated several special programs to work on parts problems," but said further improvements are needed.

"A more structured approach, periodically and systematically updating a list of serious problem parts, would enable the Air Force to take timely, aggressive top management corrective actions," the report said.

The GAO said "spare parts shortages continue to seriously limit aircraft availability; the Air Force is relying on extensive cannibalization (use of parts from grounded aircraft) to continue operations; the Air Force, even with its extraordinary efforts, has not been able to meet training and readiness objectives."

Parts failures is a major factor in the problem, the GAO said, adding: "Reliability shortfalls (parts failing faster than expected) continue to be a major cause of spare parts shortages, with other causes contributing to the problems.

"Despite extensive cannibalization to provide timely training flights, B-1B crew members have not completed required training events in the time frames necessary to be certified mission ready," the GAO said.

The shortages are affecting the availability of the bombers to carry out the Strategic Air Command's mission, the report found.