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That further step would have made it far easier to prosecute criminally anyone who knowingly provides the Houthis with money, supplies, training or other “material support.” But aid groups are already warning that it could also impede humanitarian assistance to Yemen.

The move comes as a response to, and an effort to halt, weeks of Houthi missile and drone attacks on maritime traffic off Yemen’s coast. Those attacks, which the group describes as a show of solidarity with Palestinians under Israeli bombardment in Gaza, have forced some major shipping companies to reroute their vessels, leading to delays and higher shipping costs worldwide. After issuing multiple warnings to the Houthis, Mr. Biden ordered dozens of strikes on their facilities in Yemen, although U.S. officials say the group retains most of its ability to attack commerce in the Red Sea and the Gulf of Aden.

But the designation also reflects an effort to strike a balance, one that protects the flow of desperately needed humanitarian aid to the people of Yemen, who have endured famine, disease and displacement through more than a decade of civil war after the Houthis seized the country’s capital in September 2014.

David Schenker, a former assistant secretary of state for Near Eastern affairs in the Trump administration, said the Biden administration had chosen to “split the difference.”

“I think they were trying to find a half-measure that would reflect their frustration with the Houthis while trying to minimize the potential risk of further humanitarian hardship,” he said.

Hazem al-Assad, a member of the Houthis, said in a statement that the group would not be intimidated by the United States and that the designation would not affect its operations.

U.S. officials worry that branding the Houthis a foreign terrorist organization could cause aid groups to stop sending supplies into Houthi-controlled areas of Yemen, for fear it could be deemed “material support” subject to criminal liability.

“The Houthis must be held accountable for their actions, but it should not be at the expense of Yemeni civilians,” Mr. Blinken said in his statement. He added that the United States would work with aid providers and others in the next 30 days before the designation takes effect to help them navigate the new environment.

The Treasury Department will publish licenses authorizing “certain transactions related to the provision of food, medicine and fuel, as well as personal remittances, telecommunications and mail, and port and airport operations on which the Yemeni people rely,” Mr. Blinken said.

Despite those assurances, some aid organizations were alarmed by the U.S. action.

Anastasia Moran, associate director for U.S. advocacy at the International Rescue Committee, predicted a “serious chilling effect” from the new designation, which she said would likely “affect Yemeni civilians more than anyone else.”

“We are concerned some private-sector actors, including food importers and banks facilitating transactions for humanitarian organizations, may choose to disengage altogether,” Ms. Moran said.

According to the United Nations’ World Food Program, Yemen has the world’s highest malnutrition rate, with at least 2.2 million children under the age of 5 in need of urgent treatment for the condition.

It also remains unclear whether the terrorism designation would jeopardize fragile U.S. and Saudi efforts to construct a lasting peace deal to end the conflict in Yemen. When Mr. Blinken reversed the Trump-era designations in early 2021, American officials said the move would help to facilitate dialogue between the warring parties.

U.S. officials concluded that the risks of action were outweighed by new powers they will have to sanction and prosecute front companies and intermediaries that assist the Houthis, which have developed a formidable military arsenal.

Mr. Blinken said the designation could be removed if the Houthis stopped their aggressive behavior. After Israel’s military response in Gaza after the Hamas attacks on Oct. 7, the Houthis have sought to show solidarity with the Palestinians by attacking ships they believe to be bound for Israel. The Houthis, a religiously inspired Shiite group, profess hatred of Israel.

Speaking at the World Economic Forum in Davos, Switzerland, on Tuesday, Jake Sullivan, Mr. Biden’s national security adviser, said that it was important to signal that “the entire world rejects wholesale the idea that a group like the Houthis can basically hijack the world, as they are doing.”

U.S. officials have not accused the Houthis of plotting terrorist attacks beyond the region, and the group has battled Yemen’s local affiliate of Al Qaeda, according to an October 2023 report by the Sana Center for Strategic Studies.

Yemen’s civil conflict was exacerbated by the intervention of neighboring Saudi Arabia and, for a time, the United Arab Emirates, which both regard the Houthis as dangerous proxies for Iran, which lends them financial and military support.

The conflict created a humanitarian catastrophe that Mr. Biden, as a candidate in 2020, vowed to address. Led by Tim Lenderking, the U.S. special envoy for Yemen, the Biden administration helped to secure a truce in the conflict and has been trying to help clinch a lasting peace deal.

Following a debate within the Trump administration, Secretary of State Mike Pompeo designated the Houthis a foreign terrorist organization and a specially designated global terrorist group in mid-January 2021. Iran hawks were eager to punish the Houthis for striking at Saudi Arabia and the United Arab Emirates, as well as global shipping. Officials in places like the U.S. Agency for International Development and the United Nations feared the impact of the move on humanitarian aid and said it could lead to famine.

In February 2021, less than three weeks after Mr. Biden took office, Secretary of State Antony J. Blinken reversed Mr. Pompeo’s designations. At the time, Mr. Blinken said that “the designations could have a devastating impact on Yemenis’ access to basic commodities like food and fuel,” and that the reversals were “intended to ensure that relevant U.S. policies do not impede assistance to those already suffering what has been called the world’s worst humanitarian crisis.”

Speaking to reporters at a daily briefing, the State Department spokesman, Matthew Miller, said the harsher Trump-era designation of the Houthis as a foreign terrorist organization had “a deterrent effect on groups that really wanted to provide just humanitarian aid, and nothing else.”

Mr. Schenker disputed that characterization, and expressed doubt that the new action would restrain the Houthis. “I don’t think this is going to have a great effect,” he said, adding that the group was “highly ideological” and backed by an emboldened Iran.

In a statement on Tuesday after The Associated Press first reported the planned action, Senator Tom Cotton, Republican of Arkansas, denounced Mr. Biden’s 2021 removal of the Houthis from the terrorist list as a show of “weakness.”

“Removing them from the list of terror organizations was a deadly mistake and another failed attempt to appease the ayatollah,” Mr. Cotton said, referring to Iran’s supreme leader, Ayatollah Ali Khamenei.

In a statement on Wednesday, Representative Michael McCaul of Texas, the Republican chairman of the House Foreign Affairs Committee, questioned the Biden administration’s decision not to redesignate the Houthis as a foreign terrorist organization, which he said “brings more impact and more penalties” than the specially designated global terrorist label.

Mr. Biden has been contemplating the move for at least two years, telling reporters in January 2022 that restoring the Houthis’ terrorist designation was “under consideration” after the group conducted a lethal cross-border strike on the United Arab Emirates.

Asked by a reporter last week whether he considered the Houthis a terrorist group, Mr. Biden did not equivocate. “I think they are,” he replied.

Vivian Nereim contributed reporting from Riyadh, Saudi Arabia.