Detroit ? General Motors Co. CEO Frederick “Fritz” Henderson stepped down Tuesday after the board determined that the company wasn’t changing quickly enough.

Chairman Ed Whitacre Jr. said at a hastily called news conference that he will serve as interim CEO, and an international search for a new CEO and president is planned.

Whitacre thanked Henderson for his work during a period of challenge and change, but said it is time to accelerate the pace of rebuilding the largest U.S. automaker.

The resignation comes just eight months after Henderson, 51, replaced former chairman and CEO Rick Wagoner, who was ousted March 29 by the Obama administration’s government’s auto task force.

Henderson has been with GM his entire career and was the government’s choice to run the beleaguered company after Wagoner left. Whitacre, picked by the government in June to be chairman of the new GM, is considered an industry outsider, having run AT&T Inc. for 17 years.

Whitacre and the board have become increasingly active in the company’s decisions, at times challenging some of Henderson’s decisions. In November, the board voted to abandon plans to sell GM’s European Opel unit. That reversed an earlier option favored by Henderson to sell it to a consortium led by Canadian auto parts supplier Magna International Inc.