The transfer of power took place on two fronts, with President Bush summoning members of the White House staff to the South Lawn, where he pledged to make an “unprecedented effort” to ensure a smooth transition in the first handover of the presidency since the Sept. 11, 2001, attacks. Mr. Bush said he would welcome Mr. Obama at the White House on Monday, the earliest such meeting after any recent presidential election.

“We face economic challenges that will not pause to let a new president settle in,” Mr. Bush said. “This will also be America’s first wartime transition in four decades.”

Mr. Obama, who has declined to attend the president’s global economic summit meeting on Nov. 15, said he looked forward to meeting with Mr. Bush and the first lady, Laura Bush, at what might be the only get-together by the president and his successor before Inauguration Day.

“I thank him for reaching out in the spirit of bipartisanship that will be required to meet the many challenges we face as a nation,” said Mr. Obama, adding that his wife, Michelle, will join him as he visits the Oval Office and the rest of their future residence. Their two daughters will not be taken out of school for the trip.

No incoming president in modern times has been so pressured to begin governing, in effect, before he is sworn into office. With that in mind, Mr. Obama and Vice President-elect Joseph R. Biden Jr. will meet on Friday with members of a new economic advisory board.

The group, assembled to offer wide-ranging advice, includes the billionaire investor Warren Buffett; Mr. Summers and his predecessor as Treasury secretary, Robert E. Rubin; Paul A. Volcker, a former Federal Reserve chairman; and Eric E. Schmidt, the chief executive of Google.

Image Representative Rahm Emanuel of Illinois, shown with Barack Obama during the campaign, has accepted an offer to become White House chief of staff. Credit... John Gress/Reuters

Participants will also include Mayor Antonio R. Villaraigosa of Los Angeles and Gov. Jennifer M. Granholm of Michigan.