WASHINGTON — Cass R. Sunstein, who wielded enormous power as the White House overseer of federal regulation, came to Washington to test his theories of human behavior and economic efficiency in the laboratory of the federal government. Now he is departing with a record that left many business interests disappointed and environmental, health and consumer advocates even more unhappy.

Mr. Sunstein, 57, who projected an air of disheveled academic detachment while becoming one of the Obama administration’s most provocative figures, announced Friday that he was leaving government to return to Harvard Law School.

Applying a cost-benefit analysis to his reviews of proposed rules, he said his goal was simply to make the nation’s regulatory system “as sensible as possible.”

His critics saw it differently.

“Cass Sunstein is the most well-connected and smartest guy who’s ever held the job,” said Rena Steinzor, president of the Center for Progressive Reform and a professor at the University of Maryland Carey School of Law. “But he’s also done untold damage.”