The Biden administration is preparing to announce Friday that it will alter Trump-era restrictions on federal funding of research that uses fetal tissue, according to the nation’s top health official, potentially allowing a resumption of thwarted scientific studies into covid-19 treatments, HIV and other diseases.

Health and Human Services Secretary Xavier Becerra told Capitol Hill lawmakers Thursday that the National Institutes of Health would make an announcement about what he characterized as a fetal tissue ban.

Becerra did not disclose details of the imminent policy shift. Still he made clear, as he has before, that he opposes the research-restricting rules President Donald Trump established in 2019 at the urging of abortion foes and other social conservatives crucial to the president’s political base.

“We believe that we have to do the research it takes to make sure that we are incorporating innovation and getting all of those types of treatments and therapies out there to the American people,” Becerra said during a hearing on his department’s budget before the House Appropriation’s Committee’s Labor-HHS subcommittee.

The secretary said he thought the announcement would come Friday, and an NIH spokeswoman confirmed the timing.

The immediacy of an announcement — three weeks after Becerra was sworn in — caught by surprise leading fetal-tissue researchers, scientific organizations and congressional Democrats, all of whom have been leaning on the Biden administration to undo the funding restrictions.

It is not entirely clear how far NIH will go to reorient the previous administration’s path. HHS and NIH declined to elaborate on the secretary’s remarks. And groups and individuals who have been in touch lately with administration officials on the subject said they did not come away with specifics.

Under rules approved by Trump over the objection of his HHS secretary at the time, NIH stopped providing money for fetal tissue research by scientists who are government employees. For scientists at universities and other outside laboratories, the rules did not outright ban the research, but it subjected proposed grants and contracts to a new layer of ethical review if they had already been deemed scientifically worthy of funding. An ethics advisory board, which convened once last summer and then disbanded, was stocked with known abortion opponents. It recommended rejecting all but one of 14 proposals it reviewed.

In theory, the Biden administration could reverse both parts of the rules, one part or modify a portion — for instance, leaving in place an ethics review for outside research proposals but selecting board participants who were more ideologically balanced.

“Any progress would be very helpful,” said Lawrence S.B. Goldstein, a senior researcher at the University of California at San Diego, the only member of the Trump administration’s ethics advisory board who has used fetal tissue in his work.

Restricting fetal tissue research became a cause for the religious right, because the research relies on cells from elective abortions. No evidence exists that women have been motivated to have an abortion by the prospect that fetal tissue could be donated for use in studies.

The role of fetal tissue in biomedical research extends to the 1950s, when Swedish researchers developed a polio vaccine by using fetal cells. In the late 1980s, scientists devised the technique of breeding mice with deficient immune systems and transplanting into them small amounts of immune system tissue from aborted fetuses. These “humanized” mice grow the equivalent of a human immune system.

They have become crucial lab animals in studying several major diseases, including therapies for HIV, cancers, neurological problems, sickle cell disease and eye disorders. NIH, by far the largest funding source for biomedical research in the United States, has paid for most of this work.

In academic research labs, the Trump administration’s restrictions have caused disruptions, changing some scientists’ paths and prompting them to rethink the projects for which they pursued NIH funding. For graduate students, the rules prevented them from winning training grants if any of their work relied on fetal tissue.

Early in the coronavirus pandemic last year, a senior immunologist at an NIH laboratory in Montana was blocked from pursuing possible treatments for covid-19, the disease caused by the virus, because his research relied on fetal tissue.

Last fall, when he was California’s attorney general, Becerra led a coalition of nearly two dozen state attorneys general in writing a letter to HHS and NIH, arguing that federal health officials should reject the recommendations of the fetal tissue ethics advisory board, which had ruled against almost all of the proposed grants and contracts. Alex Azar, who was HHS secretary at the time, did not act on the recommendations, thus allowing them to stand.

In a statement from his attorney general’s office at the time, Becerra noted that Trump had spoken enthusiastically about having been treated with a monoclonal antibody therapy made by Regeneron Pharmaceuticals when the president was hospitalized for several days in the fall with covid-19.

“What he failed to mention,” Becerra said, “is that Regeneron was tested in cells derived from fetal tissue. . . . Continued efforts to block funding for future fetal tissue research would put unnecessary and ill-advised limits on the scientific research we need now to combat covid-19 and ensure all Americans have access to the best, most innovative treatment for the virus.”

In January, a week before Trump left office, his administration’s health officials proposed further changes that would tighten the ability of university and other outside researchers to use fetal tissue in their work.

That proposed regulation would forbid any federal grant money to be used to acquire human fetal tissue from elective abortions. It also would limit the places where such tissue could be obtained: federal or state-run facilities and academic medical centers, but not many of the clinics where abortions tend to be performed.

The proposed rule falls within a broad review the Biden administration is conducting of all rules issued at the end of the previous administration.

In early January, a coalition of dozens of universities and organizations representing scientists, medical specialties and patients with certain diseases wrote to President Biden. The letter urged him to revoke the Trump restrictions once Biden became president and to commission a report on the value of research with human fetal tissue.

“We are confident that an independent and rigorous evaluation of the scientific and ethical merits of [human fetal tissue] research would find that it will continue to advance scientific research and contribute to the development of new treatments,” the letter said.

Since Biden took office, at least three scientific organizations have talked or met with federal health officials, as recently as this week, echoing the encouragement to take away the Trump restrictions according to an official of one group, who spoke on the condition of anonymity because the conversations were private.

On Tuesday, 26 House Democrats wrote to Becerra advising him to “immediately revoke” the Trump administration’s restrictions. Calling the Trump policy “politically motivated and unnecessary,” the letter said the research limits “continue to threaten scientific and medical advances by blocking intramural researchers from using the material and discouraging extramural researchers from pursuing research with it.”

One of the letter’s authors, Rep. Mark Pocan (D-Wis.), was the subcommittee member who asked the secretary at Thursday’s hearing whether he planned to lift the restrictions.

Replying that NIH would be making its announcement, Becerra said, “you’ll want to keep your ears open for that.”