With the financial crisis looming as a priority of his term, President-elect Barack Obama sought to put his imprint on efforts to stem the turmoil as he introduced his economic team on Monday, nominating Timothy F. Geithner as Treasury secretary and Lawrence H. Summers to head the White House Economic Council.

By naming a team deeply experienced in dealing with financial crises — Mr. Geithner was heavily involved over the weekend in the efforts to stabilize Citigroup — Mr. Obama underscored his determination to assure Americans and foreign investors that he would aggressively step into a leadership vacuum in Washington during the transition.

Moreover, by pledging that his economic team would begin work “today” on recommendations to help middle-class families as well as the financial markets, the president-elect sought to convey an impression of continuity and coordination, so that his administration can “hit the ground running.”

The president-elect also announced that he had chosen Christina D. Romer to head his Council of Economic Advisers and Melody Barnes as director of his White House Domestic Policy Council. Ms. Romer is an economics professor at the University of California, Berkeley, while Ms. Barnes is a longtime aide to Senator Edward M. Kennedy of Massachusetts.