OTTAWA — 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 e-mail 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.

Stiff competition from the Apple iPhone and phones using Google’s Android software drastically eroded RIM’s share of the American smartphone market to about 9 percent in the third quarter of 2011 from nearly half the market two years earlier, according to Canalys, a market research firm based near London. The company’s stock price reflected that by dropping about 75 percent in the last year.

But while Mr. Balsillie and Mr. Lazaridis, who have become the targets of some disgruntled shareholders, are stepping aside, investors and others looking for changes in the company’s strategy may be disappointed.