The court-martial at Beale Air Force Base north of Sacramento of an airman accused of trying to sell military secrets to Soviet agents has been delayed at least a month because the defendant fired his three attorneys. Airman 1st Class Bruce Ott, 26, an administrative clerk with the top-secret SR-71 spy plane squadron stationed at Beale, was granted permission by Judge Col. Howard Sweeney to dismiss his attorneys. Sweeney also approved the selection of Ott's new attorney, Lt. Col. William K. At Lee Jr. of Bolling Air Force Base near Washington. Sweeney recessed the proceedings indefinitely after At Lee indicated that it would take him at least a month to prepare his case. Ott had sent a letter to Lt. Col. James P. Swanson, the base staff judge advocate, requesting that his three attorneys be removed because of "irreconcilable differences."