The B-2 Stealth bomber, unveiled last fall after more than a decade of secret work, will not fly before late spring or summer, the Air Force said Friday.

Acknowledging reports that the schedule for the first flight was in jeopardy, the service said that because of "an aggregation of minor system checkout problems, the B-2's first flight is now expected to be in the late spring or early summer time frame.""Routine systems checkout of the B-2 Advanced Technology Bomber is continuing," the Air Force added. "After its first flight, the B-2 will undergo extensive testing at Edwards Air Force Base, Calif."

When the Air Force made its first announcement last summer about an unveiling for the unusual "flying wing" plane, it confidently predicted the aircraft would be ready for its first flight in the fall of 1988.