Millicent D. West, the District’s homeland security director, resigned Tuesday, citing the ongoing federal investigation that led to a guilty plea by former D.C. Council member Harry Thomas Jr.

West said she stepped down, effective immediately, “to ensure the work of the agency can carry on without any distractions. . . . It’s in the best interest of the city and in the best interest of the agency.”

In a brief interview with The Washington Post, West said: “There’s an ongoing investigation. It’s not advisable for me to talk about right now.”

West, who described her departure as voluntary, is not accused of any wrongdoing.

Thomas pleaded guilty last month to stealing more than $350,000 in public funds between April 2007 and August 2009 to pay for expensive cars, trips, clothes and meals. The money was funneled through the D.C. Children and Youth Investment Trust Corp., which provided funds to nonprofits that federal prosecutors said then kicked back money to Thomas.

West, whose resignation was first reported Tuesday by the Washington City Paper, was the trust’s president and chief executive from the summer of 2008 until then-mayor Adrian M. Fenty (D) appointed her to lead the Homeland Security Emergency Management Agency in November 2009.

Marshall D. Banks, founder of Langston 21st Century Foundation, and Jimmy Garvin, the foundation’s program director, also pleaded guilty last month. According to federal prosecutors, Thomas helped steer trust funds to the foundation, which provides educational programs to children. Langston then gave checks for $306,000 to two entities Thomas controlled.

According to documents released by prosecutors, a separate $110,000 in trust funds went to the D.C. Young Democrats for a ball at the John A. Wilson Building celebrating President Obama’s inauguration.

West has previously said she suggested to Thomas and his chief of staff at the time that they find another organization to accept the trust funds because she was wary of giving a check to a political group.

Paperwork filed by the group did not acknowledge the ball.

West said in an earlier interview that she saw no wrongdoing and believed “the money was being used for a celebration calling young people together to celebrate a historic moment.”

Pedro Ribeiro, director of communications for Mayor Vincent C. Gray (D), said West submitted her resignation letter Tuesday morning. He said he was not aware of Gray asking for the resignation.

In the letter, West wrote that “given the current distractions, I believe that this is the best decision for both my family and the District.”

West, who earns $165,000 a year as homeland security director, was one of the city’s top managers who survived the transition between the Fenty and Gray administrations.

When West was nominated in 2009, several council members initially balked at Fenty’s selection because her résumé was short on security experience and she lacked clearances that would allow her to communicate with federal agencies.

But she wooed council members and was confirmed.

“She did well at HSEMA,” said Council member Phil Mendelson (D-At Large), chairman of the Committee on Public Safety and the Judiciary. “The rap against her when she was nominated by Mayor Fenty was that she did not have experience, and she didn’t have experience. I thought she could learn, and she did.”

West was a good director, Mendelson said. But “she’s in the best place to know how distracting it [the investigation] was getting,” he said. “Her name has been in the news.”