WASHINGTON — House Democrats signaled on Monday that they would press ahead with plans to have staff lawyers question Attorney General William P. Barr on Thursday, despite his threat to skip the much-anticipated hearing on the work of Robert S. Mueller III if Democrats stick by that format.

The chairman of the House Judiciary Committee, Representative Jerrold Nadler of New York, announced a Wednesday committee vote on whether to allow lawmakers to turn over a half-hour of questioning per side to staff lawyers, an unusual arrangement for such a high-stakes hearing, though not one that violates any rules. Democrats are expected to easily win the vote, raising pressure on Mr. Barr to give up his demand that the questioning come only from lawmakers.

The confrontation between the committee and the attorney general has been weeks in the making and is part of a broader escalation of hostilities between the Trump administration and the Democratic-controlled House. The conclusion in recent weeks of the investigation by Mr. Mueller, the special counsel, and the expansion of House Democrats’ investigations into Mr. Trump’s business and his presidency have only caused tensions to flare.

“It’s not the business of a witness to try to dictate to a congressional committee what our procedures for questioning him are,” Mr. Nadler told reporters on Monday evening, adding that Mr. Barr seemed to be “very afraid” of sustained questioning by staff. Previously, Mr. Nadler had pledged to issue a subpoena to compel Mr. Barr’s testimony if necessary.