Google confessed it tried unsuccessfully to team up with Facebook, as the search giant adapts to a shifting tech landscape and strives to maintain growth.

Google Executive Chairman Eric Schmidt said at a conference on Tuesday that social networking site Facebook had rebuffed its entreaties to make a deal, while acknowledging he had not pushed hard enough to address the rising threat posed by Facebook during his tenure as CEO.

“A CEO should take responsibility,” he said. “I screwed up.”

Schmidt, who ended his 10-year run as CEO in April and handed the reins to 38-year-old Google co-founder Larry Page, made the comments at a conference organized by the blog AllThingsD.

Google is the world’s No.1 search engine. But it’s under threat from upstarts such as Facebook and Groupon, while the emergence of new gadgets has spurred a growing rivalry with iPhone-maker Apple.