WASHINGTON — At the request of the White House, the General Services Administration chief, Lurita Alexis Doan, resigned Tuesday night as head of the government’s premier contracting agency, ending a tumultuous tenure in which she was accused of trying to award work to a friend and misusing her authority for political ends.

“It has been a great privilege to serve our nation and a great President,” Ms. Doan said in a statement released yesterday morning by the agency.

A White House spokesman was not immediately available for comment.

Ms. Doan’s resignation came almost a year after Rep. Henry Waxman, a Democrat of California, chairman of the House Oversight and Government Reform Committee, said he believed Ms. Doan could no longer be effective because of the allegations about her leadership.

Mr. Waxman’s committee began investigating Ms. Doan after stories in the Washington Post showed that she had approved a $20,000, no-bid arrangement last July with a business run by a friend and had tried to reduce the budget of the agency’s inspector general.

Ms. Doan had been under scrutiny by the inspector general, Brian Miller, as well as members of Congress and the U.S. Office of Special Counsel, which protects federal employees from prohibited personnel practices.

The committee investigation turned up evidence that Ms. Doan might have violated the Hatch Act in January 2007 by asking political appointees how they could “help our candidates” at an agency briefing conducted by a White House official, according to several of the appointees present for the briefing.

After a more extensive probe, the Office of Special Counsel concluded that those remarks violated the Hatch Act.

The act generally prohibits employees of federal agencies from using their positions for political purposes.