Republicans and Democrats in Congress condemned a plan President Trump is weighing to send Afghans who aided the American military campaign against the Taliban to the Democratic Republic of Congo.

Lawmakers in both chambers and both parties said they instead wanted to see Mr. Trump restore a congressionally mandated program he blocked that allows eligible Afghans who have undergone security vetting to settle in the U.S. and have a pathway to permanent residency.

“I’m still supportive of the process,” said Senator Mike Rounds of South Dakota.

“For those individuals that helped our young men and women, once they’ve been vetted thoroughly, I have no objections to them being in the United States,” he added.

The president is considering forcing as many as 1,100 Afghans currently living in limbo on a former U.S. military base in Qatar to choose between relocating to Congo or returning home to live under the Taliban.

Democrats condemned the plan as a shameful retreat on a promise made to Afghans who worked as translators, guides and in other key roles that they would be granted a safe haven in the United States.

“Exiling them to a country they’ve never lived in or sending them to certain death at the Taliban’s hands is a cowardly betrayal,” Senator Chris Coons, Democrat of Delaware, said on social media.

Senator Jeanne Shaheen of New Hampshire, the top-ranked Democrat on the Foreign Relations Committee, said in a post on social media that it was “unconscionable” to send the Afghans, including women and children, back to the Taliban or to a country burdened by humanitarian crises.

“Congress must be united against this inhumane plan,” she added.

Gregory W. Meeks of New York, the senior Democrat on the Foreign Affairs Committee, noted that many Republicans had previously been supportive of allowing Afghan allies to stay in the United States, saying lawmakers had fought “in a bipartisan way to get them here, once properly interviewed and screened.”

But G.O.P. lawmakers who had advocated granting visas to Afghans who aided the U.S. shrank from the issue last year when the president froze a special program to provide them after the shooting of two National Guard members in Washington by an Afghan national.

“The problem that remains is that Donald Trump and Stephen Miller have wrongfully demonized Afghan immigrants,” said Representative Jason Crow of Colorado, a Democrat and former Army Ranger who served in Afghanistan and has led bipartisan authorizations of visas for Afghans. “Republicans are afraid to push back on that.”

Still, G.O.P. members said Wednesday they did not support the plan, which the State Department could carry out without congressional approval, to hand over Afghans evacuated by the United States to Congo. That country is already burdened by more than 600,000 refugees, according to the United Nations.

“We made promises to those fighting by our side to bring them to the U.S.,” Representative Don Bacon, Republican of Nebraska, said in a statement. “We should keep our promises.”

“This issue is personal to me,” Representative Zach Nunn of Iowa, a combat veteran who fought in Iraq and Afghanistan, said in a statement. “My office is seeking clarification from the State Department on these reports. America must keep its commitment to those who served alongside us.”

Lawmakers were caught off guard by the report this week that the State Department was in talks with the Congolese government to accept the Afghans as refugees, but have taken no immediate action to persuade the president to pursue an alternate resettlement option.

The State Department has given Congress no information on whether it plans to issue the thousands of remaining visas to Afghans with pending applications. Some Republicans said they want to see Mr. Trump continue the program.

Representative Joe Wilson, Republican of South Carolina, whose son served in Afghanistan, said in an interview that American forces had worked “with their Afghan brothers.”

“Those that helped America really should be brought to America,” he added, “because people certainly risked their lives.”

Senator Lindsey Graham, Republican of South Carolina, suggested he also opposed the Congo plan.

“If they’re people who helped us, that would be in a different category,” he said.

But a majority of Republicans have stayed silent as Mr. Trump has denigrated Afghan immigrants in the wake of the shooting last year that killed one National Guard member and severely injured another. The shooter had been allowed entry into the United States under former President Joseph R. Biden Jr., and later granted asylum by the Trump administration.

Many Republicans have said they support Mr. Trump’s closed-door policy for all Afghans, and are not pressing the administration to give out the visas Congress had authorized.

“I err on the side of protecting American citizens,” said Representative Derrick Van Orden of Wisconsin, a Republican running for re-election to one of the most vulnerable House seats.