The battle of titans between Microsoft Corp. and Google Inc. over the future of the Internet is about to get even hotter.

Microsoft is in talks to buy a minority stake in the popular social-networking Web site Facebook Inc., a sign of a new urgency by the software giant to jump-start its online business at a time when Google is widening its lead in the fast-growing Internet-advertising business. As part of its catch-up program, Microsoft also has quietly granted broad powers to an executive recently hired from outside the company, who is expected to help shake up the software giant's online business.

Microsoft in recent weeks approached Facebook with proposals to invest in the startup that could value the fast-growing site at $10 billion or higher, said people familiar with the matter. If those talks bear fruit, Microsoft could purchase a stake of up to 5% in the closely held startup, at a cost in the range of $300 million to $500 million, the people said.