The National Archives and Records Administration, which calls itself the country’s record keeper, apologized on Saturday for altering a photo of protesters at the 2017 Women’s March that blurred out references critical of President Trump.

“We made a mistake,” began a statement the archives released on Saturday.

The photo of protesters holding signs was part of an exhibit, “Rightfully Hers: American Women and the Vote,” which examined the struggle of women to gain the right to vote.

But signs critical of the president that appeared in the photo — including one that said “God Hates Trump” — were doctored to blur out Mr. Trump’s name, according to The Washington Post, which first reported on the alterations.

Initially, in a statement to The Post, an archives spokeswoman defended the decision and said “modifying the image was an attempt on our part to keep the focus on the records.”

“As a nonpartisan, nonpolitical federal agency, we blurred references to the president’s name on some posters, so as not to engage in current political controversy,” the spokeswoman, Miriam Kleiman, said.

But by Saturday afternoon, three museum officials were seen turning around the photo display, which was a lenticular image that from one perspective showed the 2017 Women’s March and from a different perspective shimmered to a 1913 photo of a women’s demonstration on Pennsylvania Avenue.

The display was positioned so that only a blank canvas could be seen. Officials then posted a statement to the public that also apologized for the alterations.

“In a promotional display in this spot, we obscured some words on protest signs in a photo of the 2017 Women’s March,” the statement said. “This photo is not an archival record held by the National Archives but one we licensed to use as a promotional graphic. Nonetheless, we were wrong to alter the image.”

“As the National Archives of the United States, we are and have always been completely committed to preserving our archival holdings, without alteration,” the statement said.

The controversy unfolded as tens of thousands of women gathered in Washington and other cities on Saturday for the fourth Women’s March.

Hundreds of thousands of protesters, galvanized by the 2016 election of Mr. Trump, came to Washington in January 2017.

They also marched in cities across the country, holding signs about issues as diverse as abortion, sexual assault, equal pay, voter suppression and environmental protection.

One of the photos of the Washington march, taken by Mario Tama, a photographer for Getty Images, showed a sea of protesters holding signs criticizing Trump, The Post reported.

The National Archives, which featured the photo in its exhibit, blurred Mr. Trump’s name on a sign that originally read “God Hates Trump.” Another sign “Trump & GOP — Hands Off Women” also has the word Trump blurred out, The Post reported.

A sign with the word “vagina” was also blurred and the word “pussy” was erased from another sign. The references to the female anatomy were a rebuke of Mr. Trump’s comments about women in a 2005 recording that captured him boasting how he used his celebrity status to force himself on women, even groping their private parts.

Those words were altered because the museum has many young visitors and there was concern they might be inappropriate, Ms. Kleiman told The Post.

Rinku Sen, a president of the board of directors for the Women’s March, on Saturday called the alterations a “symbol of the degradation of democracy.”

“The National Archives are our public historians and historians are not meant to change history but to report it,” she said. “To me, it says that censoring women is a thing that people think they can do.”

The decision was criticized by historians and archivists who said changing the photo was a violation of public trust.

“Museums, archives, and stewards of our historic artifacts should absolutely never change or alter visual or written content in primary sources,” said Rhae Lynn Barnes, a professor of American Cultural History at Princeton University. “That is something totalitarian governments do.”

She added: “American history is hopeful and uplifting and triumphant, but it’s also dark and disturbing. Our job is to hold both of those truths and tensions together and properly contextualize the past so current and future generations can make up their own minds about the significance of what happened and empower themselves.”

Archivists follow a strict code of ethics that forbids them from altering any images put into the public record, said Kathleen Roe, who was an archivist for 40 years at the New York State Archives, where she served as director of archives and records management.

The National Archives decision to display an altered photo is “really disappointing” and could undermine the faith of the public in archivists in general, she said.

“We are charged with providing access to the record as it exists not to the record as we wish it would exist or how it should be made to look for certain situations,” Ms. Roe said. “If there is any place that you should be able to go to for the record as it was recorded it is in government archives.”

The “Rightfully Hers” exhibit “examines the relentless struggle of diverse activists throughout U.S. history to secure voting rights for all American women,” the archives said in its description of the exhibit.

The exhibit features more than 90 records, artifacts, photographs and other items meant to capture the advances of women as they struggled for decades to secure the right to vote. The exhibit opened in May and is scheduled to run through January 2021.

A Post reporter, Joe Heim, noticed the photo during a chance visit to the museum, he said on Twitter.

Ms. Sen said the altered images would likely infuriate women and encourage them to continue protesting the Trump administration.

“We’re here to represent ourselves directly and exercise democracy directly, and we’re not going to be shut down,” she said.

Leigh Vogel contributed reporting.