President Trump has promised to invoke a wartime production law first used to churn out bullets, tanks and other weaponry during the Korean War but former Defense Department officials from Republican and Democratic administrations say it could take more than a year to bear fruit.

A growing chorus of politicians in recent days have expressed hope that American industry will rally for a different kind of war, churning out ventilators, protective gear and basic medical supplies that are in desperately short supply as medical providers across the country battle the deadly virus classified as a pandemic.

But analysts and former defense officials say the efforts so far could have little effect on a medical device industry that is already producing in overdrive mode. Even the most aggressive tools at the administration’s disposal — nudging carmakers or aerospace factories to start making ventilators — could take more than a year to achieve results, the former Defense Department officials told The Washington Post.

An executive order on Wednesday gave companies legal cover to prioritize production of ventilators and protective gear, but analysts say device manufacturers are already doing that. The Trump administration has so far balked at implementing a separate provision that could entice nonmedical manufacturers such as car companies to get involved.

In a tweet on Wednesday, Trump said he would only do so in a worst-case scenario, adding: “Hopefully there will be no need, but we are all in this TOGETHER!”

Then, on Friday, Trump told Senate Minority Leader Charles E. Schumer (D-N.Y.) in a phone call that he would trigger the act after Schumer urged him to “get ventilators and other important medical equipment to those who need it,” a Schumer spokesperson told Politico. It remains unclear which provisions of the act the White House plans to use.

Fully activating the Defense Production Act could allow the administration to use public funds to give manufacturers a boost through grants, contracts or loan guarantees. That could include luring nonmedical manufacturers to get into the business of producing ventilators, something the British government is reportedly pursuing.

Elon Musk suggested on Twitter that one of his companies would make ventilators if there were a shortage, prompting a wave of responses that can best be characterized as, “Well, there is a shortage, so make them.”

The government could even commandeer civilian airplanes to transport supplies or workers or deploy the Defense Department’s logistics network.

But experts worry that building new production centers or retrofitting manufacturing plants would take too long, even with a massive outlay of public funds.

Bill Greenwalt, who oversaw the Pentagon’s procurement and industrial planning in the Bush administration, said the efforts Trump took this week “should have occurred months ago.”

Greenwalt said investing in machinery and other government equipment to expand the ventilator production industry “at best would take a year or longer to do.” Getting an automaker to produce ventilators would probably take 18 months, he said. Even then, the necessary raw materials might not be available as other countries scramble to address their own shortfalls.

“I think we will find out that our industrial base is not capable of producing what we need, as I expect much of it has been outsourced to China and elsewhere,” Greenwalt said.

Eric Fanning, who heads the Aerospace Industries Association, said the ability of a nonmedical company to start producing ventilators would be easier for some industries than others. Fanning added that the first step is an information-gathering process to determine which companies could contribute.

“Clearly, for some facilities, it would be a heavy lift,” Fanning said. “You’ve got equipment that is focused on a specific task, you’ve got workers that are trained to do something very specific.”

Wes Hallman, a retired Air Force colonel who is senior vice president for policy at the National Defense Industrial Association, said such a turnaround would take “a matter of months,” in the most optimistic scenario, to start producing the needed health-care products.

Companies that already make ventilators appear to be moving as fast as they can, raising questions about whether federal financing would significantly change the equation.

Union officials at a General Electric plant in Madison, Wis., say they are pursuing a “lightning-fast attempt” to build as many ventilators as possible over the next 90 days. The factory is moving from one and a half to three shifts as the company seeks to increase its output, said Alex Hoekstra, an official with the International Association of Machinists and Aerospace Workers.

“There’s no company I can think of in the industrial base that isn’t pulling out all the stops,” said Brett Lambert, who managed the Obama administration’s Defense Production Act policy.

Others are concerned that the federal government has not taken the initial steps of giving industry specific marching orders.

Kelly Magsamen, a former Obama administration official who worked in the White House and the Pentagon, said it is hard to expect the commercial sector to act before the Trump administration lays out its requirements and sends manufacturing orders.

Others advocate for a more targeted approach. Andrew Hunter, a former congressional Democratic staffer and Obama administration procurement official, said the fact that automakers do not have FDA-approved ventilators could be an obstacle.

Alluding to Musk’s suggestion that one of his companies could make ventilators, Hunter said: “He’s probably right, but is a doctor really going to want to hook a patient up to a device that hasn’t been tested?”

A more likely scenario would have existing manufacturers keep producing their own FDA-approved ventilator models, Hunter said, and have the government or other companies provide them with needed equipment or manpower. The act should be used “like a scalpel, not a bazooka,” Hunter said.

Some envision a stronger role for government in guaranteeing purchases ahead of time.

Frank Kendall, who served as undersecretary of defense for acquisition, technology and logistics in the Obama administration, said that the Defense Production Act “is a tool they should definitely use” in the Trump administration and that it could help in major ways if used effectively.

One option, he said, is for the government to buy manufacturing equipment needed by companies already making ventilators to boost production. Another is to provide tooling for companies that can convert to making needed products. The law gives the government certain authorities, which Trump has not activated, to install equipment in private factories.

“What you also want to do is give companies the certainty that they are going to get paid for whatever they do, and you do that through ordering directly,” said Kendall, now a senior fellow at the Center for American Progress. The Defense Logistics Agency is best suited to handle the mission, he said.

Trump has previously said the government should not play that role. In a Thursday news conference, the president pushed back on the idea that the federal government should be responsible for shipping products to where they are needed. He said the responsibility should fall to state governors.

“Governors are supposed to be doing a lot of this work,” Trump said. “The federal government is not supposed to be out there buying vast amounts of items and then shipping. … You know, we’re not a shipping clerk.”

State officials, meanwhile, say they need federal guidance. New York Gov. Andrew M. Cuomo, a Democrat, said that his state is already “shopping for ventilators” in China and elsewhere but that the federal government “can actually play a very constructive role” using the Defense Production Act.

Michigan Gov. Gretchen Whitmer, also a Democrat, said “swift and clear guidance” would help the situation, and Sen. Gary Peters (D-Mich.) said on MSNBC’s “Morning Joe” on Friday that his state is ready to start turning shuttered car factories into manufacturing centers for masks and other needed items but that he needed the president to fully trigger the Defense Production Act.

David Berteau, president of the Professional Services Council, a trade association for government contractors, said the government can be doing more to leverage the “surge capacity” it already has.

“Industry is up to doing way more than the government has called on them to do. Industry has surge capacity that needs to be tapped.” That includes production and “providing personnel for tasks that government workers are not available to do.”

Correction: A previous version of this report misnamed the governor of New York.