REDMOND, Wash. – Microsoft Corporation’s chairman, Bill Gates, said yesterday he will gradually give up his day-to-day duties at the company to concentrate on the charitable work of the Bill & Melinda Gates Foundation.

Mr. Gates, 50, will continue as the company’s chairman after transferring his duties over a two-year period.

“This was a hard decision for me,” said Mr. Gates, who founded the world’s largest software company with childhood friend Paul Allen. “I’m very lucky to have two passions that I feel are so important and so challenging. As I prepare for this change, I firmly believe the road ahead for Microsoft is as bright as ever.”

Microsoft Chief Technical Officer, Ray Ozzie, will immediately assume Mr. Gates’s title as chief software architect and begin working with Mr. Gates on overseeing all software technical design.

Chief Technical Officer Craig Mundie will immediately take the new title of chief research and strategy officer and will work with Mr. Gates in those areas. Mr. Mundie also will partner with general counsel Brad Smith to guide Microsoft’s intellectual property and technology policy efforts.

Mr. Gates is ranked by Forbes magazine as the world’s richest man, with an estimated wealth of about $50 billion. That great wealth, he said, also brings great responsibility, and he repeated his often-spoken desire to give away the bulk of his fortune to charity. The Gates Foundation focuses on education and global health needs.

“Just as Microsoft has taken off in ways I never expected, so has the work of the foundation,” he said.

In January 2000, Mr. Gates assumed the role of chief software architect and Steve Ballmer took over the role of chief executive officer. Mr. Ballmer remains responsible for all day-to-day operations and the company’s business strategy.

The world “has had a tendency to focus a disproportionate amount of attention on me,” Mr. Gates said, when in reality, Microsoft is a company with an extraordinary depth and breadth of talent.