Alex M. Azar II, the health secretary, raised the prospect of invoking a Korean War-era law to expand production of materials for national security purposes in a potential coronavirus outbreak.

WASHINGTON — The Trump administration may use a 70-year-old law to speed up the manufacturing of medical supplies before a coronavirus outbreak, Alex M. Azar II, the health secretary, said on Friday, a seeming acknowledgment that the virus poses a threat beyond the reassurances of President Trump.

The Defense Production Act, passed by Congress in 1950 during the Korean War, allows the president to expand production of the materials for national security purposes. Mr. Azar said that the federal government could move to expedite certain contracts, including for supplies like face masks, gowns and gloves. Mr. Azar has said that 300 million of a type of mask known as N95 are needed for the emergency medical stockpile for health care workers.

“I don’t have any procurements I need it for now, but if I need it, we’ll use it,” Mr. Azar told reporters at a White House briefing on the administration’s request to Congress for emergency funds to respond to the virus.

Mr. Azar’s cautionary tone echoed warnings from officials with the Centers for Disease Control and Prevention earlier this week. But they contrasted with efforts this week by Mr. Trump and other administration officials to minimize the likelihood of a serious outbreak.

“I feel very confident, and our people are doing a fantastic job,” Mr. Trump said Friday afternoon as he left for a campaign rally in South Carolina. “We haven’t seen an increase, and people are getting better. Almost everybody that we see is getting better.”

Mr. Azar said that “the situation may worsen, and we may need to mitigate its spread in the United States.” If cases of the coronavirus began spreading widely, he said, those showing mild symptoms should stay home rather than seek help at hospitals, to avoid the risk of overcrowding health facilities.

Mr. Azar’s remarks appeared to reflect a recognition that the outbreak may reach a newer and more dangerous phase. In addition to his comments about the government stockpiling protective equipment and about how people should seek medical care in the case of a wider outbreak, he also raised the possibility of school closures.

“It might make sense to close a school or certain schools or take other measures like that,” Mr. Azar said. “Every option needs to be on the table as we assess the situation, but it depends on the circumstances.”

The health secretary appeared on Friday in his role as the head of a task force overseeing the government response to the virus. On Wednesday, Mr. Trump appointed Vice President Mike Pence to manage that response, leading to confusion about who was in charge of preparations for a potential outbreak.

If the Trump administration does invoke the Defense Production Act, it would not be the first time in recent years. The administration activated powers under the act to restore power grids and supply food and water in states and territories hard hit by the 2017 hurricane season. Past presidents have used it to ward off blackouts by sending emergency electrical power and natural gas.

A senior law enforcement official who has been briefed by Homeland Security officials, along with law enforcement officials around the country, said using the law would raise a difficult question for the future: How will the government define which emergencies warrant the speeding up of manufacturing?

At the White House briefing on Friday, Mr. Azar also addressed concerns about the limits of testing those who are showing symptoms. Only 12 laboratories outside of C.D.C. headquarters in Atlanta are currently capable of testing for the virus, and faulty test kits sent by the C.D.C. have stalled efforts in states trying to monitor patients. Hawaii this week began working to acquire kits from Japan.

Fewer than 500 people in the United States have been tested for the virus so far, according to the C.D.C. On Wednesday, Mr. Trump insisted that his administration was “testing everybody that we need to test” and “finding very little problem.”

Mr. Azar said on Friday that 1,000 more test kits were being sent to California. Two new cases of the virus have surfaced there this week, and officials have so far uncovered no clear contact between them and other infected people they are tracking, raising the possibility that the disease is circulating locally, passing from person to person. Late Friday, health officials in Oregon and Washington State confirmed their own cases of unknown origin.

On Capitol Hill, lawmakers raised the alarm, flooding federal agencies with letters asking for additional information on how local governments should prepare, on the impact on the southern border and about allegations raised in a whistle-blower complaint this week that federal staff had been dispatched to coronavirus quarantine sites without adequate preparation or supplies

“Like everyone else, I want to know what the facts are,” said Senator Patty Murray of Washington, the top Democrat on the Senate Committee on Health, Education, Labor, and Pensions, in an interview.

The inspector general for the Department of Health and Human Services said on Friday that it would begin a “comprehensive review” of the federal government’s coronavirus response, accelerating a process that had already been underway. Mr. Azar said he had been unaware of the concerns raised in the whistle-blower complaint before this week.

Investigators were eyeing the health agency’s repatriation of American citizens, its treatment of quarantine sites and its hospital preparedness program, a spokeswoman for the inspector general’s office said.

“Because of the heightened concern, we had already been planning to look into this and do a review,” said Tesia Williams, the spokeswoman. “We began to get additional information on top of that.”

But a Friday morning briefing with House members appeared to do little to assuage some of the concerns and frustration about how prepared the federal government was to respond to the outbreak in the United States.

“The question I asked was, ‘What assurances do we have that proper protocols were followed during the federal quarantine?’” said Representative Mark Takano, Democrat of California. The answer, he said, “was not as responsive as I would have liked.”

Four House Democrats from California — Mr. Takano, John Garamendi, Scott Peters and Jimmy Gomez — pressed for an additional briefing with health officials about the possible spread of the virus. Representatives Takano, Garamendi and Peters represent districts where there are cases of unknown origin or exposed people who have been quarantined, and Mr. Gomez’s office was the first to learn of the whistle-blower complaint.