WASHINGTON — As President Biden last month defended his decision to end the U.S. military presence in Afghanistan, he delivered a promise as old as the war itself to the Afghans who had risked their lives to assist American troops.

“Our message to those women and men is clear: There is a home for you in the United States, if you so choose,” the president said. “We will stand with you, just as you stood with us.”

But his decision not to begin a mass evacuation of Afghan interpreters, guides and their relatives earlier this year has left thousands of people in limbo, stranded in a country now controlled by the Taliban after 20 years of war.

Even before Mr. Biden announced the withdrawal of U.S. troops, his administration rejected frantic calls from lawmakers and activists to evacuate Afghans, who now find themselves in jeopardy.

Then this summer, Afghanistan’s president, Ashraf Ghani, implored Mr. Biden to hold off on evacuations until U.S. forces were gone for good, fearing that the image would undermine confidence in his government.

Mr. Biden instead took steps to streamline a visa system plagued with backlogs, even though it was never intended for the mass transfer of people in a short amount of time. And in the United States, some officials were expressing concerns about potential political blowback over an influx of refugees.

Taken together, the administration’s actions left Mr. Biden’s promise largely unfulfilled last weekend and led to searing scenes at the Kabul airport, where Afghans clung to the sides of departing American planes. And they raised questions about whether an administration that has said it would prioritize human rights abroad has abandoned the Afghans it depended upon most, dimming the United States’ traditional global image as a sanctuary for the persecuted.

The president on Wednesday defended the U.S. withdrawal and said he did not see a way to leave Afghanistan without “chaos ensuing.” In an interview with ABC News, he was asked whether the exit could have been handled better.

“No, I don’t think it could have been handled in a way that we’re going to go back in hindsight and look — but the idea that somehow, there’s a way to have gotten out without chaos ensuing, I don’t know how that happens,” Mr. Biden said. “I don’t know how that happened.”

But critics said the administration was squarely to blame.

“The failure to evacuate our allies rests solely in the hands of the Biden administration, who ignored veterans and advocates, even when they offered detailed plans on how evacuation to U.S. territory could be managed,” said Chris Purdy, the project manager for the Veterans for American Ideals program at Human Rights First.

Since 2002, the United States has employed Afghans to assist its troops, diplomats and aid workers. Many of those people were threatened, attacked or forced to flee their homes as a result of their work, prompting Congress in 2009 to establish a visa program specifically for those who had helped the U.S. government, as well as their immediate relatives.

The program is separate from the process typically used by those fleeing persecution or torture. About 18,000 people are in the process of applying for the visas, and those applicants have at least 53,000 relatives who would be eligible to join them. Despite a congressional mandate that the United States process the visas in nine months, thousands have faced long delays for vetting.

The Biden administration has evacuated about 2,000 of the applicants to military bases since mid-July, according to the State Department. It is preparing to evacuate another 800.

In a series of meetings and calls since March, including before Mr. Biden announced the U.S. withdrawal, lawmakers and resettlement officials warned the White House and the State Department that the situation required an urgent response — one that could not be addressed by the special visa program, which took too much time, according to resettlement and former government officials who spoke on the condition of anonymity to describe internal discussions.

The special visa program requires applicants to clear extensive levels of vetting and provide evidence of their work — documents that can be hard to obtain for families who have been forced to flee their homes. The Biden administration has blamed the previous administration for exacerbating the delays through “extreme vetting” requirements.

The calls for swift evacuations picked up even as the Biden administration deployed additional staff members in Washington and at the embassy in Kabul to address the backlogs. One official said the administration cut through the bureaucracy by slashing in half processing delays that totaled an average of two years when Mr. Biden came into office, lobbying Congress to expand the number of visas and waiving requirements for medical examinations.

More than 300 Afghans applicants were resettled in the United States in June compared with about 200 in January, according to the White House. The number of Afghans welcomed in July, when the administration began evacuations, jumped to more than 1,650.

Even in the best of circumstances, however, vetting refugees is enormously time-consuming. The prospect of thousands of Afghan refugees coming to the United States — rather than to other countries — raised concerns among some government officials, who argued that it would open up the White House to political pushback, according to administration officials and other people familiar with the matter.

Some lawmakers, such as Representative Matt Rosendale, Republican of Montana, have expressed concerns about expediting the vetting process.

“Now we’re going to develop a procedure with which we can vet thousands of individuals and just relocate them to the United States?” he said in an interview. “Once they’re settled here, they can bring additional family members here. One kind deed does not make an ally.”

Leaving behind Afghans — especially women and girls — could have significant political implications for Mr. Biden.

“The day they start killing women in Afghanistan: That is their political nightmare,” said Michael A. McFaul, a professor of international studies at Stanford University and a former ambassador to Russia during the Obama administration. “Those numbers that support withdrawal are incredibly soft. If women who took U.S.A.I.D. money begin to be arrested or killed, that support will diminish quickly, and people will be outraged by the president.”

Refugee advocates say the Afghans’ sacrifices for the United States should outweigh any potential political risk that comes with mass resettlement.

“It’s pretty rich, considering we trusted these people enough to put the lives of U.S. forces in their hands but not to bring them to U.S. soil,” said Becca Heller, the executive director of the International Refugee Assistance Project, which is working with the State Department to assist the Afghans.

In the days since the Taliban took control of Afghanistan, Mr. Biden has approved an additional $500 million for “unexpected urgent refugee and migration needs of refugees, victims of conflict and other persons at risk as a result of the situation in Afghanistan.”

The administration also put out a call for volunteers throughout the government to help with processing the Afghan visas. An email from United States Citizenship and Immigration Services described the opportunity as an “extraordinary initiative” and encouraged any employee in any position to apply.

The Pentagon’s top two leaders said on Wednesday that the United States was committed to evacuating all Americans who want to leave Afghanistan, as well as Afghans who helped the war effort and were cleared to enter the United States.

“We intend to evacuate those who have been supporting us for years, and we are not going to leave them behind,” Gen. Mark A. Milley, the chairman of the Joint Chiefs of Staff, told reporters. “And we will get out as many as possible.”

At a news conference, however, neither General Milley nor Defense Secretary Lloyd J. Austin III would assure safe passage to the airport for Americans, Afghans and other foreigners outside the perimeter.

“The forces that we have are focused on security of the airfield,” Mr. Austin said. “I don’t have the capability to go out and extend operations currently into Kabul.”

The administration has insisted that its actions in recent months were calculated decisions, not missteps.

It relied on intelligence showing that a Taliban takeover was 18 months away, and officials have acknowledged that they underestimated the pace of the Taliban advance when considering whether to carry out evacuations. Many Afghans were close to the end of the visa pipeline, leaving officials with an inaccurate sense that the administration had enough time to continue to rely on the visa program.

The administration has also emphasized Mr. Ghani’s request over the summer to hold off on evacuations until after the Americans were out of Afghanistan.

“The Afghan government and its supporters, including many of the people now seeking to leave, made a passionate case that we should not conduct a mass evacuation lest we trigger a loss of confidence in the government,” Jake Sullivan, the national security adviser, said at a White House news briefing on Tuesday. “Now, our signaling support for the government obviously did not save the government, but this was a considered judgment.”

The administration was hesitant for months to move the Afghans to military bases in the United States or its territories, such as Guam, preferring to move them to other countries instead, according to administration officials and people familiar with White House and State Department deliberations. Many of the evacuees would have only temporary protection while their visas were processed. If they were denied visas, they would need to apply for asylum or another form of protection in the United States — immigration programs that Republicans have seized on to attack Mr. Biden.

“They are basically in the United States, and there’s not really an effective way to say no in an effective manner,” said Barbara L. Strack, a former chief of the refugee affairs division at Citizenship and Immigration Services during the Bush and Obama administrations. “The government worries about the ‘no’ cases.”

One former contractor for the United States who was relocated from Jalalabad strolled aimlessly outside a housing complex in eastern Maryland on Monday afternoon, familiarizing himself with his new surroundings.

The man, who asked to be identified only as Masoon out of fear for his safety, said he had made it from Kabul to Maryland after a 20-hour stopover at the Fort Lee military base in Virginia. Although he arrived safely with his wife and five children, his parents and sisters remained in Jalalabad.

“I’m very happy here,” Masoon said, “but I am not happy about my family.”

He added: “The Taliban is in Jalalabad, and what can I do about that situation? It is really a dangerous thing.”

Masoon said he had lost all contact with them since he departed Afghanistan less than two weeks ago.

Eileen Sullivan, Jennifer Steinhauer, Michael D. Shear, Eric Schmitt, Catie Edmondson and Lara Jakes contributed reporting from Washington.