WASHINGTON — House Democrats said on Monday they would vote next week to hold Attorney General William P. Barr and the former White House counsel Donald F. McGahn II in contempt of Congress for defying subpoenas related to Robert S. Mueller III’s report, even as they announced a new series of hearings meant to refocus attention onto its findings.

The twin announcements were the party’s latest attempts to kick-start stalled investigations into accusations of malfeasance by President Trump and his administration and to try to force key witnesses resisting their oversight demands into compliance. But they also underscored that in the face of Trump administration opposition, House lawmakers have been left with few good options to investigate accusations that could eventually lead to impeachment.

“This administration’s systematic refusal to provide Congress with answers and cooperate with congressional subpoenas is the biggest cover-up in American history, and Congress has a responsibility to provide oversight on behalf of the American people,” Representative Steny H. Hoyer of Maryland, the No. 2 House Democrat, said as he announced the contempt votes.

The first of the new hearings, scheduled for next Monday before the House Judiciary Committee, is not exactly the showcase Democrats had hoped for. Rather than questioning Mr. Mueller, the special counsel, himself — or Mr. McGahn, for that matter — the committee’s first star witness will come from another era and presidential scandal entirely: John W. Dean of Watergate fame. Still, the session will allow lawmakers on the panel traditionally charged with carrying out impeachment proceedings to fully air Mr. Mueller’s findings for the first time.