Exit of division heads and agency’s general counsel comes as Chairman Mary Schapiro is also stepping down. (Evan Vucci/ASSOCIATED PRESS)

Three top officials at the Securities and Exchange Commission announced this week that they plan to leave the agency, following the lead of SEC Chairman Mary L. Schapiro, who plans to step down Dec. 14.

Robert W. Cook and Meredith B. Cross — who each head one of the SEC’s five divisions — said they are on their way out, as did Mark D. Cahn, the agency’s general counsel. Cook will remain for a “transitional period,” but Cross and Cahn plan to leave at the end of the year and return to the private sector, according to SEC statements.

They are leaving at a time when the SEC is struggling to reckon with Wall Street in the aftermath of the financial crisis and keep up with technology that has transformed the trading landscape — areas that all three were intimately familiar with in their respective roles.

At federal agencies, the exodus of senior leaders is not unusual after a presidential election. Schapiro was widely rumored to be leaving for months before the election, and a few of her closest advisers exited by the time she made her plans official. But turnover always raises questions about a potential “brain drain” and disruptions as a new crew settles in to fill the empty slots.

In this case, the transition should not be too bumpy for now, because the incoming chairman, Elisse Walter, has served on the commission since 2008 and spent many years on the SEC staff before then, several people who track the agency said. As for the divisions and the legal office, the “pick-and-shovel work” will continue with or without their chiefs, said Scott Kimpel, a partner at the Hunton & Williams law firm.

“There is a deep bench of deputies to the directors who are career civil servants,” said Kimpel, former counsel to SEC Commissioner Troy A. Paredes, a Republican. “One of them will get the nod to take over until a permanent successor is found.”

Cross has served as the corporate finance division’s director since June 2009 and played a lead role in shaping regulations tied to the Dodd-Frank financial regulatory overhaul measure. About a year later, Cook took over as head of the trading and markets division, where he helped craft the regulatory responses to the May 2010 flash crash. Cahn has served as general counsel since February 2011 after two years as deputy general counsel.