A high-stakes debate raged inside the Trump administration on Friday over the fate of the veteran U.S. attorney investigating New York’s attorney general, Letitia James, and the former F.B.I. director James B. Comey, according to people briefed on the situation.

Administration officials informed Erik S. Siebert, the U.S. attorney for the Eastern District of Virginia, that he would most likely be fired, but there appeared to be a last-ditch effort by some in the Justice Department to protect Mr. Siebert and the situation remained in flux, those people said.

Mr. Siebert has recently told senior Justice Department officials that investigators found insufficient evidence to bring charges against Ms. James and has also raised concerns about a potential case against Mr. Comey, according to officials.

President Trump has long viewed Ms. James and Mr. Comey as adversaries and has repeatedly pledged retribution against law enforcement officials who pursued him. The president, who has publicly called Ms. James “a crook,” has in the past expressed frustration that a prosecution against her was not moving ahead, according to a person briefed on his remarks.

A Justice Department spokesman and a White House spokesman did not immediately respond to requests for comment. A spokesman for Mr. Siebert did not comment.

Several administration officials, speaking on the condition of anonymity because they were not authorized to discuss personnel matters, described the situation as fluid, unsettled and confusing. Mr. Siebert and his top deputy were still at their desks working, and no one had been officially ordered to leave, as of midday Friday.