WASHINGTON — Senate Democrats are on the verge of moving to eliminate the use of the filibuster against most presidential nominees, aides and senior party leaders said Wednesday, a move that would deprive Republicans of their ability to block President Obama’s picks for cabinet posts and the federal judiciary and further erode what little bipartisanship still exists in the Senate.

Senator Harry Reid of Nevada, the majority leader, is poised to move forward on Thursday with a vote on what is known on Capitol Hill as the “nuclear option,” several Democrats said. Mr. Reid and the senators who have been the most vocal on stopping the Republican blockade of White House nominees are now confident they have the votes to make the change.

“We’re not bluffing,” said one senior aide who has spoken with Mr. Reid directly and expects a vote on Thursday, barring any unforeseen breakthrough on blocked judges.

The threat that Democrats could significantly limit how the filibuster can be used against nominees has rattled Republicans. Senator John McCain, the Arizona Republican who has brokered last-minute deals that have averted a change to filibuster rules in the past, visited Mr. Reid in his office on Thursday but failed to strike a compromise.