In a long-ranging interview with Walt Mossberg and Kara Swisher, Google Chairman Eric Schmidt talked at length about privacy.

Google Inc. executive chairman Eric Schmidt said one of his biggest failures as chief executive of the search giant over the last decade was grappling with the rise of social identity services such as Facebook Inc.

In a wide-ranging keynote interview at the D9: All Things Digital conference in Rancho Palos Verdes, California Tuesday, Mr. Schmidt said Google had missed on "the friend thing"—including valuable information about who users and their friends are, which can be used to improve the information delivered to them. "In the online world you need to know who you are dealing with," said Mr. Schmidt, who became executive chairman earlier this year while Google co-founder Larry Page took over the CEO role. "I clearly knew that I had to do something and I failed to do it."

Future Google products will add social functionality, he said, such as the previously announced service rolling out to websites starting on Wednesday called "+1" which will help users recommend search results to their online social contacts.

Mr. Schmidt said the consumer Internet today has come to be dominated by a "gang of four" companies that want to be platforms for other companies: Google and Facebook, along with Apple Inc. and Amazon.com Inc. "We have never had four companies growing at the scale that those four are in aggregate," he said.

Mr. Schmidt's comments came as Google increasingly faces pressure to both partner and compete with all three of those tech titans. Mr. Schmidt said Google recently renewed its relationships with Apple for use of its maps and search services, even as Google develops Android, its alternative to Apple's iOS operating system for phones and tablet computers.

Even as Google develops its own social services, he said the company tried to partner with Facebook on search but was rebuffed.

Facebook didn't immediately respond to a request for comment.

In the interview, Mr. Schmidt also said privacy was a top concern for Google, and that he would "much rather" have a private company making decisions about consumer privacy than the government. Nonetheless, he said he generally supported some kind of privacy regulation by the U.S. government "because it would rationalize some of the questions" about the issue, meaning that it could simplify the debate.

With Google's size and dominance, Mr. Schmidt said the company expects "constant review" of its acquisitions and policies by regulators. Since he stepped down from his position as CEO, Mr. Schmidt said he has been focusing much of his energy on dealing with outward-facing public policy issues.

Write to Geoffrey A. Fowler at geoffrey.fowler@wsj.com