WASHINGTON — The former head of the Obama administration's auto task force expressed optimism Wednesday that General Motors and Chrysler could rebound and help taxpayers recoup some of their multibillion-dollar investment in the Detroit auto companies.

Steven Rattner, in a speech sponsored by the Brookings Institution, said his auto team was stunned by the dire straits of GM and Chrysler when they delved into the companies' financial books but remained confident that the overhaul of the automakers could eventually restore them to profitability.

"I think we gave them every tool, not only that we could, but every tool that they need," Rattner said at the National Press Club. "We believe that both of these companies are viable and we believe they both can earn good returns for their shareholders."

Rattner cautioned that "it will probably take time for the government to get out" of its nearly 61 percent stake of GM and 8 percent share of Chrysler. He said the task force studied similar cases and found that it took three to five years on average for a government to divest its holdings in private companies.

"No one should expect overnight turnarounds ... Be patient," Rattner said. He later told reporters, "I don't believe the government will or should conduct a fire sale."

Rattner led the auto task force as it pushed GM and Chrysler into quick bankruptcies last summer with the help of about $65 billion in federal aid.

Alan Reuther, the United Auto Workers' legislative director, said the liquidation of GM and Chrysler would have dragged down Ford Motor Co., threatening pensions and health care of 1 million Big Three retirees.