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.