Microsoft Corp. has signed an agreement to sell advertisements from outside the U.S. on Facebook Inc., beating rival Google Inc. in a closely watched contest that includes an investment by Microsoft in the social networking Web site.

Microsoft and Facebook announced that Microsoft will invest $240 million as part of Facebook’s next round of financing, which will place a $15 billion valuation on Facebook.

The Microsoft agreement comes after intense lobbying by Microsoft and Google for Facebook’s hand. In recent weeks, executives including the chief executive of Microsoft, Steve Ballmer, have courted the three-year-old Palo Alto, Calif., company, which this year expects a profit of $30 million on revenue of $150 million, according to people familiar with the company.

The deal is rooted in an online advertising boom that has turned closely held Facebook into the newest Internet darling. In recent years, large advertisers that once focused their spending on television, newspapers, and other traditional media have started shifting their spending to a host of Web sites. Google has built its fortunes on that shift and others, including Microsoft, are rushing in.

Facebook, a service that lets people set up their personal Web pages, is seen as the next big venue for placing online display ads. The company has nearly 50 million users, many of them the young audience that advertisers covet. In addition to selling ads on its own, the company over the past year has started placing ads through a deal it signed last year with Microsoft, under which Microsoft brokers banner ads on Facebook’s American site until 2011.

The deal signed yesterday is an expansion of that agreement and focuses on international versions of the Facebook service, which Facebook is now starting to open. A deal with Microsoft would allow Facebook to shift some of the burden of selling international display ads to its larger partner. Microsoft in recent years has built up a large online advertising sales force and has invested in technologies to broker advertising over the Web.

By the end of this year, Asia will account for 35% of the world’s social networking users, with 28% of users in Europe, the Middle East, and Africa, 25% in North America, and 12% in the Caribbean and Latin America, according to research firm Datamonitor PLC.

The vice president of Google, Tim Armstrong, declined to comment on any Google discussions with Facebook. “We have tremendous respect for them as a company,” he said during Google’s analyst day at the company’s Mountain View, Calif. headquarters.

The online publication CNET reported earlier yesterday that Facebook and Microsoft were close to a deal.