(This version of the January 3rd story corrects paragraph 5 to show Barr changed response after being queried by a senator)

FILE PHOTO: U.S. Justice Department building is seen in Washington, U.S., December 7, 2018. REUTERS/Yuri Gripas/File Photo

WASHINGTON (Reuters) - President Donald Trump’s pick to serve as U.S. attorney general, William Barr, got his nomination off to an awkward start by telling lawmakers he did not register for the military draft during the Vietnam War, before saying on Thursday that he had in fact signed up.

Barr, who previously served as attorney general under President George H. W. Bush, told the Senate Judiciary Committee he had incorrectly described his draft record in biographical materials he submitted ahead of his confirmation hearings.

“I have not served in the U.S. Military. I was born in 1950 and was not required to register for selective service,” he initially wrote on a questionnaire released by the committee.

Historians told Reuters that Barr would have been required to register for possible military service when he turned 18, a time when the government was drafting roughly 300,000 people per year to serve in Vietnam.

Barr changed his response after being asked about it by one of the senators on the committee, a Justice Department representative said.

“I registered for the selective service at 18, as required, and was subject to the draft,” Barr wrote on Thursday in a letter to Republican Senator Lindsey Graham, the new chairman of the committee, and Senator Dianne Feinstein, the top Democrat.

Men who do not register for the draft face fines of up to $250,000 and a prison term of up to five years. They also are barred from most federal jobs, according to the Selective Service System, which registers men for possible compulsory service.

“I can’t imagine a scenario in which (Barr) would not have been required to register,” Kansas University history professor Beth Bailey said.

Barr, 68, said he initially told lawmakers he had not registered because he is now too old for compulsory military service.

He will have a chance to explain the mix-up when he appears before the Judiciary Committee for confirmation hearings on January 15 and 16.

Many prominent U.S. politicians -- including Trump -- have struggled to explain why they did not serve in the Vietnam War, which bitterly divided the United States.

At Barr’s confirmation hearings, Democrats are expected to question him about his willingness to protect the independence of Special Counsel Robert Mueller’s investigation into possible ties between Trump’s 2016 presidential campaign and Russia.

Barr criticized Mueller’s conduct of the probe in a lengthy memo submitted to the Justice Department last year, prompting Senate Democratic Leader Chuck Schumer last month to call on Trump to find a new nominee for attorney general.

Deputy Attorney General Rod Rosenstein said last month that Barr’s memo has had no impact on Mueller’s investigation.

The investigation has secured more than 30 indictments and guilty pleas, and has spawned at least four federal probes. Trump has repeatedly criticized it as a “witch hunt.”

If confirmed by the Senate, Barr would take over from Matthew Whitaker, who has been serving in an acting capacity since Trump forced out Jeff Sessions in November. Whitaker had been Sessions’ chief of staff.