A federal repository of emergency supplies is far better equipped, its top administrator said, than during the early days of the coronavirus pandemic when states desperate for such materials were stymied by a beleaguered stockpile.

Compared with the start of the pandemic nearly 1½ years ago, the National Strategic Stockpile contains 35 times as many N95 respirator masks, according to Dawn O’Connell, the Department of Health and Human Services’ new assistant secretary for preparedness and response.

Appearing Tuesday during her first congressional hearing since being sworn in three weeks ago, O’Connell said the stockpile, which her agency oversees, has 17 times as many protective gloves and eight times as many other types of masks. All the N95 masks are now made in the United States, she said, rather than relying on imports that were subject to global competition when federal officials sought to build up supplies during spring 2020.

Because of money allotted for the stockpile in coronavirus relief packages adopted by Congress, “we’re beginning to see some progress,” O’Connell told members of the Senate Health, Education, Labor and Pensions Committee.

Sen. Richard Burr (R-N.C.), the committee’s ranking Republican, cautioned that it will be difficult to prevent the stockpile from becoming depleted again over time, because lawmakers tend to have relatively short memories and may be reluctant to keep providing money for manufacturing supplies.

“We sort of forget about the last incident that we went through,” Burr said, “and . . . we look at it and say, ‘Well, why are we funding to keep the lights on in this N95 mask facility we don’t need anymore?’ ”

The debate over the stockpile’s durability occurred during the most recent in a series of hearings convened by the panel to assess the federal government’s response to the pandemic and how to better prepare for public health crises.

Senior Biden administration health officials stressed, as they have been saying lately, that the three coronavirus vaccines authorized for emergency use in the United States provide good protection for most people who receive them, even against the highly transmissible delta variant.

Centers for Disease Control and Prevention Director Rochelle Walensky testified that the delta variant now accounts for an estimated 83 percent of U.S. cases of covid-19, the illness caused by the virus, that are analyzed using genomic sequencing. She called that a dramatic increase from 50 percent during the first week of this month and said the percentage is higher where vaccination rates are relatively low.

Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, described the delta variant as “formidable” because of its ability to transmit from person to person “in an extraordinary manner.” He said it has been detected in at least 90 countries.

Still, he said the three vaccines being used in the United States — developed by Pfizer-BioNTech, Moderna and Johnson & Johnson — are highly effective against the variant, providing more than 90 percent protection against serious illness that leads to hospital stays or death.

He reiterated that studies are underway to determine how long the vaccines confer their maximum protection and whether booster shots may be needed. An advisory committee to the CDC is scheduled to discuss Thursday whether a booster is warranted for a small percentage of U.S. adults whose immune systems have been compromised by cancer treatment, organ transplants or other medical circumstances.

Sen. Rand Paul (R-Ky.) reprised accusations against Fauci, saying the government’s top infectious-disease expert lied about whether NIH funded research at a virology institute in Wuhan, China, the city where the virus was first detected.

“As you are aware, it is a crime to lie to Congress,” Paul said, contending that Fauci had misrepresented facts during previous testimony before the committee.

The running dispute between the two men is part of a broader debate over whether the virus emerged from nature or from a laboratory. When Paul renewed the accusations Tuesday, Fauci once again shot back.

“Senator Paul, you do not know what you are talking about, quite frankly. I want to say that officially,” Fauci said, his voice raised. “You are implying that what we did was responsible for the deaths of individuals. If anybody is lying here, senator, it is you.”