WASHINGTON — Three years ago, American investigators produced a 15,000-page analysis of atrocities committed in 2017 against the Rohingya, an ethnic Muslim minority group in Myanmar. The report documented survivors’ accounts of gang rapes, crucifixions, mutilations, of children being burned or drowned and of families locked inside their blazing homes as Myanmar’s military sought to exterminate them.

That was not enough to convince the State Department during the Trump administration that the United States should officially proclaim the Rohingya to be victims of genocide and crimes against humanity.

But now that the military, the Tatmadaw, has overthrown Myanmar’s civilian government, current and former American officials and human rights activists are demanding that President Biden do what the Trump administration would not: Formally hold the country’s military accountable for genocide and compel international protection of the Rohingya.

“The same military leaders who orchestrated atrocities against the Rohingya have seized power in a violent coup against the elected government,” Senator Edward J. Markey, Democrat of Massachusetts, told Secretary of State Antony J. Blinken at a Senate hearing in early June.

Mr. Markey asked when the State Department would decide whether the atrocities amounted to genocide, and though Mr. Blinken described a “very much actively ongoing” review, he would not predict when it might be resolved. He said the State Department was working with the United Nations “to try to collect and preserve evidence that will be very important” to conclude if genocide was committed.

Some American allies — including Canada, France and Turkey — have already declared the monthslong rampage in 2017 against the Rohingya as genocide. The 57-nation Organization of Islamic Cooperation filed legal action against Myanmar in 2019, accusing it of violating the U.N.’s Genocide Convention.

Mr. Biden has made fostering democracy and protecting human rights pillars of his foreign policy, and in April went so far as to declare century-old atrocities committed against Armenians by the Ottoman Empire as genocide.

But he has stopped short of a genocide designation on behalf of the Rohingya because of a continuing internal debate that has left the administration torn over what impact it would have and how forcefully the United States should be engaged in the protracted conflict between the Tatmadaw and Myanmar’s citizens, according to three people familiar with the discussions.

Diplomats who work on human rights issues have pushed for a genocide declaration. But State Department officials who oversee East Asia policy fear that it could turn other Burmese against the United States for appearing to favor the Rohingya — who are widely reviled in Myanmar and have been denied basic rights by their own government — over people who are now also being brutalized by the military.

“What is the catalyst that’s needed right now for people to focus on Burma as this continues?” said Anurima Bhargava, the chairwoman of the U.S. Commission on International Religious Freedom, a bipartisan panel that makes policy recommendations to the federal government.

She cited “deepening atrocities” that are threatening hundreds of thousands of Myanmar’s people — including the Rohingya — by the Tatmadaw. “That would make a genocide determination easier right now, given who’s in power and, certainly in some ways, be a way in which to highlight what it is that this particular military has done over the course of many years,” Ms. Bhargava said.

The Biden administration was quick to declare the military’s takeover of Myanmar’s government in February as a coup, and in May committed to sending $155 million in aid to Rohingya refugees in what Mr. Blinken described as a continuing effort to promote “peace, security and respect for the human rights and human dignity of all people in Burma, including Rohingya.”

The 2018 report detailing the attacks against the Rohingya left little doubt to investigators hired by the State Department that the Tatmadaw had committed genocide and crimes against humanity.

It was based on evidence compiled by investigators and lawyers with the Public International Law & Policy Group, which the State Department hired in early 2018 to assess the violence in Myanmar’s northern Rakhine State in 2017. After interviewing more than 1,000 Rohingya refugees who had fled to camps in neighboring Bangladesh, the team documented more than 13,000 grave human rights violations, in findings that Daniel Fullerton, who managed the investigation, described as “staggering.”

The final analysis that Mr. Fullerton wrote and submitted to the State Department in July 2018 amounted to what he called the most expansive investigation into the crimes against the Rohingya.

Two months later, the State Department quietly released its final report, drawing on the evidence that Mr. Fullerton’s team had compiled. It detailed the planned and coordinated nature of widespread violence against the Rohingya in Rakhine State, resulting in mass casualties, including against religious leaders who had been singled out.

But it conspicuously did not conclude that Myanmar’s military had committed genocide or crimes against humanity.

At a U.S. Commission on International Religious Freedom hearing on genocide in May, Mr. Fullerton said the evidence his team gave the State Department provided “reasonable grounds to believe there was an intent to destroy the Rohingya.”

He added, “We thus face the question of: If the U.S. can’t, or we won’t, make a determination when it actually has so much reliable information about what happened, when can it?”

Jalina Porter, the State Department’s deputy spokeswoman, declined to comment when asked why those findings had failed to convince diplomats that genocide had been committed, calling it a decision made by the Trump administration.

In its final days in office, the Trump administration issued a genocide declaration on behalf of ethnic Uyghur Muslims in northwest China, blaming Beijing for a systematic and brutal repression of the minority group. While few have disputed the merits of that designation, it raised questions about why the Rohingya were not similarly declared victims of genocide.

Under Mike Pompeo, President Donald J. Trump’s second secretary of state, the State Department was sharply focused on countering and containing China. With the genocide declaration, the United States this spring imposed additional economic sanctions against several Chinese officials on top of a raft of penalties that the Trump administration had already issued to punish Beijing for human rights abuses against the Uyghurs.

Mr. Pompeo’s strategy sought to isolate China among its regional neighbors, and a decade-long American push to promote democracy and the rule of law in Myanmar after a civilian government was formed in 2011 was widely seen as an effort to counter Beijing’s influence.

Priscilla Clapp, the chief of mission at the U.S. Embassy in Yangon from 1999 to 2002, said the State Department had long been mindful of trying to keep the civilian government in Myanmar “on an even keel” and help it resist being overrun by China’s ambitious Belt and Road initiative.

Issuing a genocide designation on behalf of the Rohingya against the civilian government that was in power until February — led by the Nobel laureate Daw Aung San Suu Kyi — could have disrupted those efforts and other democratic reforms, Ms. Clapp said.

“No matter how much criticism they were taking over the Rohingya issue and various other things, they were actually doing a lot to reform,” she said.

Ms. Aung San Suu Kyi has been detained by the military, including at an undisclosed location, since the Feb. 1 coup. She won the Nobel Peace Prize in 1991 for her years under house arrest to resist Myanmar’s earlier military rule.

But she also defended Myanmar from accusations of genocide against the Rohingya during a 2019 appearance at the International Court of Justice that tarnished her international credentials as a champion of human rights.

A genocide declaration by the United States could prompt economic sanctions, limits on aid and other penalties against Myanmar’s leaders. It almost certainly would increase pressure on other nations and foreign companies that have even indirectly helped the Tatmadaw remain in power.

The Biden administration has been torn over penalizing Myanmar’s state-owned oil and gas industry amid a lobbying push by California-based Chevron, which is one of three foreign operators in a massive gas field off the country’s coast. Profits from the field are one of the Myanmar military’s largest sources of revenue.

“If there’s a declaration of genocide, it at least will allow for a reconsideration by those companies as to whether or not they want to be doing business there,” said Michael H. Posner, a longtime human rights activist and former assistant secretary of state during the Obama administration.

But Mr. Posner said American diplomats in Yangon had described themselves in 2019 as “playing small ball” when trying to map out a human rights strategy in Myanmar and predicted that the Biden administration was “having a hard enough time trying to figure out where its leverage is there.”

“My view would be: When you see a genocide, when you document a genocide, anywhere in the world, and the evidence is clear, then you ought to say it, as a starting point,” said Mr. Posner, now an ethics and finance professor and director of the Center for Business and Human Rights at New York University.