Barr won’t say whether the White House was briefed on the report.

Representative Nita M. Lowey, Democrat of New York and chairwoman of the full Appropriations Committee, pressed Mr. Barr to say whether the White House has seen or been briefed on the contents of the Mueller report beyond what was in his letters about it to Congress. But Mr. Barr refused to answer.

“I’ve said what I’m going to say about the report today,” he said. “I’ve issued three letters about it. I was willing to discuss the historic information of how the report came to me and my decision on Sunday,” March 24, when he wrote a four-page letter to Congress laying out the special counsel’s top-line findings.

“But I’ve already laid out the process that is going forward to release these reports hopefully within a week,” he added. “I’m not going to say anything more about it until the report is out and everyone has a chance to look at it.”

In the past, Justice Department officials have said that Mr. Barr had not shown the White House any part of the Mueller report or briefed Mr. Trump’s team about its contents. His demurral on Tuesday raised the possibility that the situation has shifted and the White House knows more than the public or Congress about what Mr. Mueller said.

Democrats press Barr on Mueller.

Democrats who lead the House Appropriations Committee were eager to press Mr. Barr on what one called “the elephant in the room”: his handling of the highly anticipated special counsel’s report.

“The American people have been left with many unanswered questions; serious concerns about the process by which you formulated your letter; and uncertainty about when we can expect to see the full report,” Mr. Serrano said in his opening remarks.

“I think it would strike a serious blow to our system and yes to our democracy if that report is not fully seen,” he added.