Steven Rattner stepped down Monday as the Obama administration's top auto adviser, having overseen the U.S. government's unprecedented efforts to restructure General Motors Co. (GM) and Chrysler Group LLC.

Rattner plans to "transition back to private life and his family in New York City," Treasury Secretary Timothy Geithner said in a statement. Rattner wasn't immediately available for comment.

Ron Bloom, who has worked alongside Rattner on the Obama administration's auto-industry task force, will take over as the administration's chief auto adviser. Bloom is a former adviser to the United Steelworkers union.

Rattner, a former New York Times reporter and Wall Street financier, was appointed by Obama in February to lead the team advising the White House on the auto-industry rescue. He was a leading figure in negotiations among auto executives, creditors, union leaders, and other stakeholders that culminated with bankruptcy filings by GM and Chrysler.

Each auto maker exited bankruptcy protection more swiftly than independent analysts had expected. The government now owns about 60% of GM and a smaller stake in Chrysler after spending tens of billions of dollars on their restructurings.

It was never clear how long Rattner had planned to stay on board. As recently as last week, he declined to discuss his future role and that of other task force members.

He faced questions in April after news reports disclosed he was one of the executives involved with payments under scrutiny in a probe of an alleged kickback scheme at New York state's pension fund. Neither Rattner nor his former private-equity firm, Quadrangle Group, had been accused of wrongdoing at the time.

As leader of the auto task force, Rattner periodically briefed reporters on the government's plans for GM and Chrysler, answering questions more candidly than other administration officials.

Geithner called Rattner's leadership and vision "invaluable."

"I hope that he takes another opportunity to bring his unique skills to government service in the future," Geithner said.

"He has done a very good job, and he made a significant contribution to a brighter future for the auto industry," said Sen. Carl Levin, D-Mich.

-By Meena Thiruvengadam and Josh Mitchell, Dow Jones Newswires; 202-862-6629; meena.thiruvengadam@dowjones.com