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.

But Microsoft must first outgun Google, which has also expressed strong interest in a Facebook stake, according to people familiar with the matter.

The Facebook talks come as Microsoft's top management is making another significant move at its online-advertising business. The company is expected to give increasing oversight of its Internet operations to Brian McAndrews, an advertising executive who joined Microsoft just last month through its $6 billion acquisition of aQuantive Inc., an online-advertising specialist that is also part of Microsoft's strategic push. His broad mission will be to increase the number of advertisers that buy ads through Microsoft's system and Web publishers that tap into it for ads to run on their sites.