WASHINGTON  Lurita A. Doan has been forced out as head of the General Services Administration, the federal agency that oversees billions of dollars in contracts and manages thousands of government-owned buildings.

In a stormy two-year tenure as the agency’s administrator, Ms. Doan was accused of improperly mixing government business with politics and of trying to steer government contracts to her friends. Democrats in Congress said she violated the Hatch Act, which makes it illegal for government employees to take action that could influence an election.

Ms. Doan’s resignation was requested by the White House on Tuesday and takes effect immediately, the agency said Wednesday. Ms. Doan said in a statement, “It has been a great privilege to serve our nation and a great president.”

The agency said that its deputy administrator, David L. Bibb, a career employee, would take over, at least for the time being.