WASHINGTON — K. T. McFarland, the former Fox News commentator appointed by President Trump as deputy national security adviser, is expected to leave that position soon and may be nominated to be the United States ambassador to Singapore, according to officials briefed on the matter.

Ms. McFarland’s departure had been seen as likely since the forced resignation of Michael T. Flynn, the retired three-star general who was Mr. Trump’s first national security adviser. Mr. Flynn’s successor, Lt. Gen. H. R. McMaster, has been moving to put a more traditionally professional stamp on the operations of the National Security Council.

Last week, Mr. Trump signed an order restructuring the council’s “principals committee” along more traditional lines than the version he had initially put in place. It removed Stephen K. Bannon, the White House’s chief strategist and a former chairman of the conservative website Breitbart, while adding several officials Mr. Trump’s original order had left off, including the chairman of the Joint Chiefs of Staff and the directors of national intelligence and the C.I.A.

Administration officials briefed on the matter confirmed Ms. McFarland was stepping down, but said her departure would not be immediate. The officials also said her possible nomination for the ambassadorship to Singapore, while likely, had not been finalized.