SAN FRANCISCO  Mark Zuckerberg of Facebook is not stepping aside for a chief executive as Larry Page and Sergey Brin did at Google or as Jerry Yang and David Filo did at Yahoo. He is following the Bill Gates model and holding the top post as he hires a Google executive, Sheryl Sandberg, as chief operating officer.

Ms. Sandberg, currently vice president for global online sales and operations at Google, joined the search giant in 2001 and helped develop its immensely lucrative online advertising programs, AdWords and AdSense. She will join Facebook later this month to work closely with Mr. Zuckerberg, a co-founder of Facebook, the company said Tuesday.

“A big theme of this hire is that there are parts of our operations that, to use a pretty trite phrase, need to be taken to the next level,” Mr. Zuckerberg said in an interview. Ms. Sandberg will help Facebook expand overseas and develop an advertising network that will help justify its carbonated $15 billion valuation, set last year when Microsoft invested $240 million for 1.6 percent of the company. She will also oversee Facebook’s marketing, human resources and privacy departments  essentially guiding how Facebook presents itself and its intentions to the outside world.

Ms. Sandberg’s departure is a blow to Google, where she was a well-regarded executive. “Sheryl was a valued member of the Google team and we wish her well in her new endeavors,” Omid Kordestani, Google’s senior vice president for global sales and business development, said in an e-mail statement. Mr. Kordestani said David Fischer would take over Ms. Sandberg’s job. Until now, Mr. Fischer was vice president for online sales and operations, reporting to Ms. Sandberg.