WASHINGTON — President Biden came into office promising to dismantle what he described as the inhumane immigration policies of President Donald J. Trump. But for much of Mr. Biden’s presidency so far, the White House has been divided by furious debates over how — and whether — to proceed in the face of a surge of migrants crossing the southwest border. And the internal battles have not been limited to the immigration agencies.

In a meeting last summer, officials from the Centers for Disease Control and Prevention told Mr. Biden’s top aides that it was not clear there was still a public health rationale for keeping the border shut to most migrants, according to three people who attended or were briefed on the discussion.

The Trump administration had seized on Title 42 of the public health code to justify turning away most migrants at the border. When Mr. Biden took office, he said he would not apply the policy to unaccompanied minors, a change from the prior administration. In practice, many families were also let into the United States in spite of the policy.

But by last summer, the coronavirus, including the Delta variant, was already spreading wildly throughout the country. Top C.D.C. officials said it was not clear that keeping out migrants, including asylum seekers, would do much to prevent the spread of a variant already inside the United States.

That was not what some in the White House wanted to hear. Publicly, Mr. Biden and his top aides had always deferred to the C.D.C. when asked about the public health rule, saying it was entirely up to the health agency to decide how long to leave it in place.

But privately, some of Mr. Biden’s advisers were worried that lifting the restriction would invite even more migrants to the southwest border and could be seen as premature if another variant of the virus emerged. White House officials also argued that Title 42 was needed to prevent the spread of the disease along the border.

For the immigration advocates working inside the White House, it was all maddening. They had come to work for Mr. Biden to dismantle the worst policies put in place by Mr. Trump. Now they were being asked to make arguments for continuing them.

Some officials at the C.D.C. resented being blamed for keeping in place what many activists saw as a regressive border policy, according to several people familiar with their complaints.

The C.D.C. finally announced at the beginning of April that it would lift its public health border restrictions on May 23, around the time of the year when migration typically increases.

But this past week, the issue of Title 42 flared up again as Republicans and some Democrats in Congress held up Covid funding in an effort to protest the administration’s decision to lift the health rule.