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

Much of the criticism of Ms. Doan came after it became known that on Jan. 26, 2007, a deputy to Karl Rove, then President Bush’s chief political adviser, gave a briefing to employees of her agency that identified incumbent Democrats in Congress whom the Republican Party hoped to unseat in 2008, as well as Republican incumbents who seemed vulnerable to defeat.