WASHINGTON — Senate Republicans were expected again on Wednesday to block action on voting rights legislation, intensifying calls by activists and lawmakers for Democrats to finally do away with the filibuster or find themselves at a steep disadvantage in next year’s midterm elections and into the future.
For the third time this year, Republicans were poised to use the procedural weapon to thwart an attempt by Democrats to ensure access to the ballot box and counteract a raft of G.O.P.-written state laws around the country imposing new election restrictions.
Anticipating the move, President Biden, who has been criticized by progressives for not being aggressive enough on voting rights, reached out on Monday to Senate Democrats to express his support for what the White House described as a “must-pass priority.”
And at least one Democrat who had previously been reluctant to alter filibuster rules said he was ready to do so when it came to the voting measure.
“When we are talking about the fundamental operation of democracy, I have to think a Senate rule will have to be modified or give way,” said Senator Angus King, the Maine independent, saying that he would back changes to the filibuster rule if needed to pass the bill.
Under Senate rules, a supermajority of three-fifths — or 60 votes — is needed to break a filibuster and close debate on legislation, allowing it to come to a vote. In the 50-50 Senate, that effectively means that 10 Republicans are needed to join Democrats to allow major bills to advance, a threshold that has usually proved unreachable with the G.O.P. bent on stopping Mr. Biden’s agenda.
That has been the case with voting rights legislation, a version of which Republicans have blocked twice before.
Liberal activists have long pressed for Democrats to use their majority to force a change in that rule, which they could do on a simple majority vote. But they would need the backing of Senators Joe Manchin III of West Virginia and Kyrsten Sinema of Arizona, two Democrats who have said repeatedly that they would not go along with such an effort.
In a statement, the White House did not mention the filibuster or say whether Mr. Biden had discussed the matter with either senator. But the White House statement said that Mr. Biden would work to safeguard voting rights “through legislation, executive actions, outreach, the bully pulpit and all other means available.”
Jen Psaki, the White House press secretary, also steered clear of the filibuster on Tuesday but suggested that Democrats would ultimately have to find some way to advance the voting legislation, which the party regards as crucial to defanging what it sees as a concerted bid by Republicans to limit minority voting.
“If Republicans cannot come forward and stop standing in the way, if they can’t support strengthening, protecting the fundamental right to vote, then Democrats are going to have to determine an alternative path forward,” she said.
With time running short to impose changes before next year’s elections, progressive supporters of the voting rights legislation urged Mr. Biden to capitalize on his credibility as a longtime senator and push to weaken or eliminate the filibuster that is stalling his agenda.
“The president really needs to get into the mix,” said Meagan Hatcher-Mays of the group Indivisible.
Mr. King joined a handful of Democrats to hammer out the compromise with Mr. Manchin, the sole Senate Democrat who opposed a broader voting rights, campaign finance and ethics measure passed by the House and blocked by Republicans earlier this year.
The new legislation that Democrats will try to bring up on Wednesday is narrower in scope than the initial bill but would still set minimum standards for early and mail-in voting, impose new campaign finance disclosure rules and try to rein in partisan gerrymandering — all proposals Republicans oppose.
Senator Mitch McConnell, Republican of Kentucky and the minority leader, reiterated on Tuesday that he anticipated that all Republicans would oppose bringing the legislation to the floor. Mr. McConnell portrayed the effort as a political power grab by Democrats.
“This latest iteration is just another example of how they would like the federal government to take over all state elections,” Mr. McConnell said.
Should the proposal be blocked as expected, Democratic officials said they did not anticipate an immediate move to overturn the filibuster. They hoped the failed vote would show Mr. Manchin that Republicans were not interested in a bipartisan compromise on voting rights and help to persuade him and Ms. Sinema that there was no alternative for passing the legislation other than a change in rules.
Senator Chuck Schumer, Democrat of New York and the majority leader, took care to note in his remarks on the Senate floor that Mr. Manchin himself had declared earlier that “inaction is not an option” when it comes to voting rights.
“This is one place where Senator Manchin and I agree,” Mr. Schumer said. “All 49 other Democrats agree with Senator Manchin.”
Mr. King was among a group of centrists who had expressed resistance to changing the rules governing the filibuster because of potential institutional damage to the Senate.
But he said he had concluded that it might be a necessary step to protect voting rights. He said he was worried that the growing Republican acceptance of baseless claims that the 2020 presidential election was stolen from Donald J. Trump posed a grave threat to the nation’s democracy.
“Elections are the fundamental gearbox of our whole democratic system and if you devalue elections and tell people elections can’t be trusted, it basically undermines public confidence in the system and leads to the kind of manipulation you see going on in many states now,” he said. “I have decided that democracy is more important than a Senate rule.”