WASHINGTON — President Obama is planning to elevate a key national security deputy, Denis R. McDonough, to White House chief of staff, administration officials said on Wednesday, making perhaps his closest foreign policy adviser the gatekeeper to the Oval Office.

Though Mr. Obama has not made a final decision, aides said they expected an announcement early next week. Mr. McDonough’s appointment would continue the president’s practice of putting the people he trusts most in critical positions. Mr. McDonough would succeed Jacob J. Lew, another close aide whom Mr. Obama has nominated as Treasury secretary.

The appointment would also place a national security expert in a job that will require confronting a range of thorny domestic issues, including the budget, gun violence and immigration, as well as dealing with Congress — a requirement that tripped up at least one of his predecessors.

“It’s a new set of challenges for him,” said former Senator Tom Daschle, the South Dakota Democrat for whom Mr. McDonough worked before joining Mr. Obama in 2007, when he was a senator. But Mr. Daschle said Mr. McDonough had a qualification that trumped his policy background: “He has an extraordinarily close relationship with the president.”