Dr. Deborah L. Birx, President Donald J. Trump’s coronavirus response coordinator, told a congressional committee investigating the federal pandemic response that Trump White House officials asked her to change or delete parts of the weekly guidance she sent state and local health officials, in what she described as a consistent effort to stifle information as virus cases surged in the second half of 2020.

Dr. Birx, who publicly testified to the panel Thursday morning, also told the committee that Trump White House officials withheld the reports from states during a winter outbreak and refused to publicly release the documents, which featured data on the virus’s spread and recommendations for how to contain it.

Her account of White House interference came in a multiday interview the committee conducted in October 2021, which was released on Thursday with a set of emails Dr. Birx sent to colleagues in 2020 warning of the influence of a new White House pandemic adviser, Dr. Scott Atlas, who she said downplayed the threat of the virus. The emails provide fresh insight into how Dr. Birx and Dr. Anthony S. Fauci, the government’s top infectious disease expert, grappled with what Dr. Birx called the misinformation spread by Dr. Atlas.

The push to downplay the threat was so pervasive, Dr. Birx told committee investigators, that she developed techniques to avoid attention from White House officials who might have objected to her public health recommendations. In reports she prepared for local health officials, she said, she would sometimes put ideas at the ends of sentences so that colleagues skimming the text would not notice them.

In her testimony on Thursday, she offered similarly withering assessments of the Trump administration’s coronavirus response, suggesting that officials in 2020 had mistakenly viewed the coronavirus as akin to the flu even after seeing high Covid-19 death rates in Asia and Europe. That, she said, had caused a “false sense of security in America” as well as a “sense among the American people that this was not going to be a serious pandemic.”

Not using “concise, consistent communication,” she added, “resulted in inaction early on, I think across our agencies.”

And those at fault, she said, were not “just the president.”

“Many of our leaders were using words like, ‘We could contain,’” she continued. “And you cannot contain a virus that cannot be seen. And it wasn’t being seen because we weren’t testing.”

Dr. Birx became a controversial figure during her time in the Trump White House. A respected AIDS researcher, she was plucked from her position running the government’s program to combat the international H.I.V. epidemic to coordinate the federal Covid response.

But her credibility came into question when she failed to correct Mr. Trump’s unscientific musings about the coronavirus and praised him on television as being “attentive to the scientific literature.” She was also criticized for bolstering White House messaging in the early months of the coronavirus outbreak that the pandemic was easing.

Yet as outbreaks continued that year, Mr. Trump and some senior advisers grew increasingly impatient with Dr. Birx and her public health colleagues, who were insistent on mitigation efforts. Searching for a contrarian presence, the White House hired Dr. Atlas, who functioned as a rival to Dr. Birx.

“They believed the counterfactual points that were never supported by data from Dr. Atlas,” she said in Thursday’s hearing.

In one email obtained by the committee, dated Aug. 11, 2020, Dr. Birx told Dr. Fauci and other colleagues about what she called a “very dangerous” Oval Office meeting with Mr. Trump. In that session, she said, Dr. Atlas had called masks “overrated and not needed,” and had argued against testing for the virus, saying it could hurt Mr. Trump politically.

Dr. Birx claimed that Dr. Atlas had inspired Mr. Trump to call for narrower recommendations on who should seek testing.

“Case identification is bad for the president’s reelection — testing should only be of the sick,” she recounted Dr. Atlas saying.

“He noted that it was the task force that got us into this ditch by promoting testing and falsely increasing case counts compared to other countries,” she added, referring to a group of senior health officials that gathered regularly at the White House. “The conclusion was Dr. Atlas is brilliant and the president will be following his guidance now.”

In another email sent to senior health officials two days later, Dr. Birx cataloged seven ideas espoused by Dr. Atlas that she referred to as misinformation, including that the virus was comparable to the flu, that football players could not get seriously ill from the virus and that “children are immune.”

“I am at a loss of what we should do,” she wrote, warning that if caseloads kept mounting, there would be “300K dead by Dec.” The United States ended the year with more than 350,000 Covid deaths.

“I know what I am going to do,” Dr. Fauci wrote in reply. “I am going to keep saying what we have been saying all along, which contradicts each of his 7 points below. If the press ask me whether what I say differs from his, I will merely say that I respectfully disagree with him.”

In her interviews with the committee last year, Dr. Birx described regular attempts by others to undermine the weekly pandemic assessments she first sent to state and local officials in June 2020, which offered “comprehensive data and state-specific recommendations regarding the status of the pandemic,” the committee wrote in a news release.

Beginning in the fall of that year, Dr. Birx said, she began receiving “a list of changes for three or four states” each week, which sometimes involved bids to loosen mask recommendations or indoor capacity restrictions. In one instance, she was asked to soften guidance intended for South Dakota officials and remove some recommendations for the state, which had a surge in case counts at the time.

When she asked the White House to publish the reports so that Americans would know more about outbreaks in their communities, the request was denied, she told investigators. In December 2020, she told them, the White House stopped sending the reports to states unless they were requested.

Dr. Birx told committee investigators that she was asked to change the reports about “25 percent” of the time or else they would not be sent.