WASHINGTON — The Biden administration is considering whether to expand second coronavirus booster shots to adults under 50 in an effort to counter the latest, highly contagious variant, which has driven up hospitalization rates and deepened worries about waning immunity among those vaccinated or boosted at least six or so months ago.

Expanding eligibility for a fourth dose of vaccine to younger adults would require regulatory approval; more discussions with officials from the Food and Drug Administration and the Centers for Disease Control and Prevention are expected in the coming days, according to people familiar with the situation.

The administration decided in March to offer second booster doses to everyone 50 or older, along with some younger individuals who have immune deficiencies. Dr. Anthony S. Fauci, a leading infectious disease expert and the chief medical adviser to the White House, has forcefully argued for broadening eligibility to all younger adults.

Two federal officials said that Dr. Ashish K. Jha, the White House coordinator for the pandemic response, also favors that approach. The discussions were reported earlier by The Washington Post.

In an interview on Monday, Dr. Fauci said there was not enough clinical data to strongly recommend that those under 50 get a second booster shot. But he said many in that age group received their last shot in November or December, so their protection against the virus is waning.

Although it is up to the F.D.A. and the C.D.C. to decide, Dr. Fauci said, “I think there should be flexibility and permissiveness in at least allowing” a second booster for younger adults.

Other federal officials seem more skeptical and anxious to see more data to justify the decision. Some have argued that the administration should be trying harder to persuade Americans to accept the initial round of Covid vaccines, rather than pursuing diminishing benefits with those who are already at least somewhat protected.

There are also concerns that by promoting second boosters for all adults now, the administration could weaken its argument for reformulated booster shots in the fall, when it hopes to offer boosters that better combat the latest versions of the virus. The F.D.A. recently recommended that the vaccines be redesigned to better combat the fast-spreading Omicron variants of BA.4 and BA.5.

The June 30 decision came just two days after the agency’s committee of independent vaccine experts overwhelmingly voted for regulators to pursue more advanced vaccines tailored to forms of Omicron, an acknowledgment that the current shots may no longer be as protective by the time a possible fall or winter surge arrives.

The two most recent Omicron subvariants have driven up rates of hospitalization and death, though both remain far lower than at the height of the winter Omicron wave. The same subvariants have sent hospital admissions climbing in Britain, France, Portugal, Belgium and Israel.

The White House has scheduled a news briefing for Tuesday on the state of the pandemic and the threats posed by the latest Omicron subvariants.