Airline executives contend that declining accident statistics prove that flying is safer than ever. However, a number of analysts say aviation safety is eroding as the struggling major carriers cut corners on maintenance, safety inspections and pilot training. Some observers blame deregulation of commercial air transportation in 1978 for today's financial woes. They also argue that the nation's air- traffic control system has never fully recovered from the strike of 1981, when 11,400 controllers were fired. But on one point the airlines and their critics seem in total agreement -- the need to reorganize the Federal Aviation Administration, the agency in charge of air safety.