SAN FRANCISCO — Government regulators are sharing some alarming information about Facebook: They believe the online social network has often misled its more than 800 million users about the sanctity of their personal information.

The unflattering portrait of Facebook’s privacy practices emerged Tuesday in a Federal Trade Commission complaint alleging that Facebook exposed details about users’ lives without getting legally required consent. In some cases, the FTC charged, Facebook allowed potentially sensitive details to be passed along to advertisers and software developers prowling for customers.

To avoid further legal wrangling, Facebook agreed to submit to government audits of its privacy practices every other year for the next two decades. The company committed to getting explicit approval from its users – a process known as “opting in” – before changing their privacy controls.

The FTC’s truce with Facebook, along with settlements this year with Google and Twitter, is helping to establish more ground rules for online privacy expectations even as Internet companies regularly vacuum up insights about their audiences in an effort to sell more advertising.

Although Facebook didn’t acknowledge any wrongdoing in the legal papers it signed with the FTC, Facebook co-founder and CEO Mark Zuckerberg was more contrite in a blog post Tuesday.

“I’m the first to admit that we’ve made a bunch of mistakes,” Zuckerberg wrote. “In particular, I think that a small number of high-profile mistakes … have often overshadowed much of the good work we’ve done.”

Facebook has overcome its missteps in the past to emerge as the world’s largest social network and one of the Internet’s most influential companies since Zuckerberg created the website in his Harvard University dorm room in 2004.

No website has been as successful as Facebook at getting people to voluntarily share intimate details about themselves. Zuckerberg has emerged as the Internet’s chief evangelist for sharing, partly because he believes it can help make the world a better place by making it easier for people to stay connected with the things and people that they care about.

Facebook also is trying to make money by mining the personal information that it collects to help customize ads and aim the messages at people most likely to buy the products and services being promoted.

That strategy has been working well as Facebook prepares to sell its stock in an initial public offering that’s expected next year.

The company’s revenue this year is expected to approach $4.3 billion, according to research firm eMarketer, up from $777 million in 2009. The rapid growth is expected to make Facebook the biggest Internet IPO in history, topping Google’s stock market debut in 2004.