Jim Balsillie and Mike Lazaridis, who made the BlackBerry a leading business tool but then presided over its precipitous decline, said they would step down on Monday as co-chairmen and co-chief executives of Research in Motion. The two men, in developing the innovative device that was the first to reliably deliver email over airwaves, turned a tiny Canadian company into a global electronics giant. But they are stepping aside after disappointing investors and leaving customers wondering whether RIM still has the ability to compete, and perhaps even survive, in the rapidly changing markets for smartphones and tablet computers.